"un" =not. So, when you say not uncomfortable (not not-comfortable) it serves as a double negation and the not and the "un" cancel each other out, leaving you with just 'comfortable.' I've noticed they do this throughout the LSAT quite often and it can trip you up with mapping, which I think is their intended goal. I used to automatically map words like 'uncomfortable' using a 'UC' but now that I've caught on to the trick, I'll map 'uncomfortable' as '/C' I hope that makes sense. You'll catch on because they'll typically do something similar to what they did in this question where in one sentence in the stimulus they use the word 'uncomfortable' in one conditional rule and then in the next sentence in they'll use the word 'comfortable' in another conditional rule.

same