Here is the gist of what the civics mean, as I planned them.
Both Caesardom and Totalitarian imply dictatorships, and the idea I had for distinguishing the two really came from the Second Revolution mod. There, one civic was called "Personalistic" and the other was called "Totalitarian;" I borrowed the basic idea but renamed the first one in order to be more clear about what it meant, and how it differed from a totalitarian state.
The notion of dictatorship is, as always, a sticky one to convey in Civilization IV, because the player is technically always a lifelong (indeed, immortal) dictator during the game, regardless of civics. The real validity with government civics is as a way to simulate what the effects of different governments would be, as though the leader was less than absolute and enduring. However, some things do differ based upon more than just what sort of power a leader has.
The Economist Democracy Index lists both Israel and Palestine as "flawed democracies," not because there's anything wrong with their actual government structure (except that perhaps Israel should have a written constitution, but the UK does not have a written constitution either, and does alright), but probably because of the glaring religious bias in both, which colors judgement. Mexico likewise has a constitution modeled after the US, but functions less because of poor labor conditions, economic mismanagement, and similar flaws.
The core game already has tyrannical institutions represented across every category; you'd still think a country with Universal Sufferage was fairly tyrannical if it also had Slavery implemented, for example. Rather than change this theme of multiple brands of oppression, I simply wanted to modernize it, which solicited the changes. "Hereditary Rule" does not work in the modern world, where few absolute monarchies are left, nor does it really make sense in a game where leaders are immortal. "Representation" isn't valid as a milder alternative to "Universal Sufferage," because the latter has been reached in all major democracies. Hence, both democracy and dictatorship are split into two types. A "Caesar" is basically a demagogue; he rules as a dictator, but only because the people want him to. That doesn't rule out all authoritarian measures, but it at least balances the "whip-to-carrot" ratio a little more. A totalitarian may or may not have to resort to brutal measures more than a "Caesar," but has more interest in brainwashing the country to see eye-to-eye with him.
The easiest way to understand what the difference is between "authoritarian" and "totalitarian" governments, is to consider the first to be a government intolerant of certain behaviors, whereas the second is one that mandates certain behaviors. So in other words, in an authoritarian system, any behavior is probably fine so long as it doesn't threaten the government. In a totalitarian one, the government feels threatened if you don't put the dictator's portrait or something like a swastika everywhere.
Totalitarianism is therefore much less flexible, but authoritarianism in fact does not necessarily imply dictatorship. It's still possible for a democratic country to become intolerant of those who dissent from what the majority of the people decides upon. Singapore (Is it in the mod?) can be considered an authoritarian democracy. Caesardom as I interpreted it does imply dictatorship, but less as a means to keeping the people in line than as a means to streamlining the bureaucratic processes that would plague a democracy; hence the effect I gave it.
Which brings us, finally, to Technocracy, and to China. Technocracy is in my interpretation much like Plato's Republic. It isn't necessarily undemocratic, as an arguement of its advocates against democracy would likely argue that a democracy just boils down to people being misled by and electing the enlightened elite, so an enlightened elite that is good ought to be constitutionally mandated from the start. However, in the case of China, a technocracy has emerged out of two causes: One, as a secular replacement for the traditional Confucian civil service examination system, and two, due to the intentions of a communist government that understands the benefit of strong leadership to a country, but also understands the dangers of what can happen when loyalty to the leadership becomes seen as more important than usefulness to the country.
You had mentioned that the European Union was the only "country" you planned on giving the technocracy civic, and that you hadn't thought about China. They actually are not that different from one another. The European Union is a coalition of different nations; China is a multiethnic, multireligious and multicultural empire-gone-nationstate, which is part of why its leaders have always felt the need to exert firm control to keep it together. The EU may consist of democracies (to varying degrees; I still dislike the political scene in much of Eastern Europe), but its leadership isn't really all that democratic. China, in a similar fashion, has democratic elections on the local level, as well as some autonomous regions like Hong Kong, but not popular elections of the national government.
At the same time, it is a myth that China has made no political reforms. Their adoption of many market reforms alone proves that they've renounced the old Cultural Revolution motto that "It's better to red than expert," and points to the arguement for them being a technocracy, but beyond that, there is the fact that under the new constitution, their chief executives are still not popularly elected, but they also are not unchecked in power, and do not serve for life. For that matter, they also certainly don't have their portrait plastered everywhere. Your arguement that China is still a one party dictatorship really doesn't point towards using either Totalitarian or Caesardom civics for them, because those represent one man dictatorships, and furthermore, China is a one-party dictatorship only because that's how, in fact, checks and balances manifest themselves in China. To get power in China usually requires joining the Communist Party, but now the Communist Party is admitting a great deal of types who aren't particularly "communistic." Hence, there is no longer perfect unity just because only one party can legally exist in China, because that party's ranks have swelled to contain many rival factions; in China, they call them "cliques."
So yes, China's government fits best with the Technocracy civic. The view of their government as undemocratic has less to do with its actual structure (fairly similar to Western republics now) than it does with its relation to the people (still forceful and detached), so this situation is better replicated with State-Censored media, Collective labor, and Martial Law.