NON combat units only have an attack of 0.
Your use of capital letters might confuse some newer players with NONE and NON units. "non-combat" units do have an attack of 0; and the game in turn uses that valuse of 0 for lots of other purposes, too. But from his context, I think Duke may have been referring to the specific non-combat units of Spy and Diplomat (and the combat units of Nuke and Cruise Missile).
In theory, these have defense of 0 and should immediately lose any battle. In practice, there is a possibility they can win an individual hit point resolution when the game is computing the series of results to determine the victor of a battle. This occurs when the random number generator chooses 0... this will result in a hit point deduction from the attacker. The net effect can be observed when you attack barb leaders with weak attack units, esp when those leaders are on mountains. A horseman, for example, will often lose 2 or 3 hit points ("health") when attacking the barb leader (actually a diplomat) on a mountain... yet the defense factor is "Zero".... The odds are astronomical, but possible, a diplomat can defeat even a battleship
The proper resolution and odds of combat in Civ II is probably the single most complex issue in Civ II. This is tangled quite a bit because the easily accessible "sources" like the Prima Guide are not really correct...
The folks like SlowThinker (I can't recall the others right off) have done lots of awesome work in figuring out how the Civ II combat system really works, and particularly in some cases, the results might be quite surprising and conter-intuitive.
BTW, the game itself does not "damage points" that you were talking about. I won't open the whole FP, HP discussion, except to say that
Since combat resolution is a quagmire to accurately explain in full, a starting point for those that might wish to pump iron with their mind might want to begin with this thread of Slow Thinker:
With all that said, the actual (exact) computations are really probably a moot point for most players... Civ is such a fun game, but there is quite a bit going on behind those graphics