I suppose the thing is, on the Colbert sketch he comes up with more Korean names that are working on the very same trick, only executed with the 'right' sort of name-structure. He also projects it from a position of obvious satire, his show is unabashedly satirical in nature. Because of that, that kind of thing is tolerated more because it is being presented from a 'you were warned' standpoint.
I think confusing Chinese names with Korean names is ignorant, and I can even understand how it could be considered casual racism, but never leave too small a margin for just 'dumb'. I'd consider it more of a cultural faux-pas than an act of casual racism, it's not really assigning a stereotype based on an assumption, more a case of simply not knowing the difference between the two cultures names.
Edit : And I'll note, a Cultural Faux Pas is not anything less offensive and unpleasant than Racism is, I'm not trying to play down the act, I simply have concerns that, as far as the name thing was concerned, it seems missing the barb of intent, and assumption based more on simple lack of knowledge than anything I could define as hurtful. I suppose it could be argued that the ignorance is not a defence, or even that it was the tool with which the Racism was implemented, but I'm not sure it is feasible for every person to understand every structure of every naming system, which is what would be required in order to avoid it.
I do see Karas' concern, of some intern thinking to himself 'I need some Korean names' and then just grabbing 'Asian Sounding' words out of the air, I can see how that is belittling to bundle all Asian cultures up into one, when there are vast differences between them, but I suspect he was no more aware that he was making Chinese names than he was aware he was not making Korean ones.