I don't mean to speak for him, but I think his resentment of Russia stems from the fact that the Czech republic was under Russian domination for 45 years after ww2.
There were bad things in it and there were good. There was Soviet propaganda, which criticized and depreciated the West, capitalism and their influence. And there is Western propaganda now, which has been doing visa versa since those times. Soviet communist bloc is no longer there, though Western capitalist one is still there, and it still has those things which were introduced to resist communist idea before the 1917 year and after, some of which are bluff from the beginning, contradicts logic and facts, like modern liberalism, political correctness, multiculturalism and limitless consumerism. Though these ideas result in problems and contradictions today, and more and greater in the future to come, the West still perceives reality through the prism of them—at least mass media and most people do so, I don't think true politicians have ever deceived themselves.
The same prism and propaganda are used or surface when it comes to Russia or Soviet Era. By default bad things only and bad opinions are preferred in the question of Soviet influence on other countries, "occupation" of them or the situation in the Union itself. I do not know that much about Czechoslovakia to say whether bad or good, fair or unfair prevailed there, but I know about other countries and ex-republics, that there were more good and fair, though regardless of that people are taught, media and politcians concentrate solely on bad things when talking about those times (even in Russia), they invent myths and lies, reaching total absurdity.
The idea, for example, that Soviet regime was exclusively Russian and modern Russian Federation is the one to blame or the one to feel imperialistic looking to the past is absurd. Those who had made revolution in Russia, came to power and were in power in USSR, those people were of different ethnic and place-of-birth backround, Ukrainians, Georgians, Jews, Stalin was Georgian, Khruschov was Ukrainian. Local athourities of the republics were of local nationals predominantly. Countries, which made hatred of Soviet/Communist Era almost their national politics (and I can name them exactly: Poland, Lithuania, Latvia and Estonia) had had those communists and soviets among their populace and politicians before Soviet Union came there, along with resistance to communists/Soviets there was support of them, and even anti-Communist repressions.
If your country was under Polish domination, a mere puppet state ruled from Warsaw, I'm sure you'd have ill feelings towards Poland too.
Our country
was under Polish domination in the past

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