I'd say, just for now at least, look at the bigger picture. So far this discussion only focuses on two things... a) you two had sex, and b) he didn't kiss you at the time. If you want to decide what all this means... these can't be the only two factors that it all boils down to. If you believe this guy has liked for a period of time, and you got to the point of sex somehow, then there must have been some other interaction of some kind between you. Other than this one particular event... what has been his general demeanor towards you?
I have been in this situation a few times... and there's no hard fast rule for what anything like this means. I've had a couple of different guys noticeably avoid kissing me during sex, and yeah, in each case they did turn out to be interested in sex but not especially interested in me. And even if I could have accepted casual flings at the time, when a guy is going out of their way to constantly remind you that "this is only casual" in petty little ways like that... it's a bit of a turn off, so I end anything like that. (Which strangely enough caused a backflip further down the track both times, and I got chased after no end when I was no longer interested lol... but anyway, I disgress).
On the other hand, I myself have avoided kissing guys during sex. Not often, and the only reason being that when you're doing stuff that brings on a lot of heavy breathing your mouth can get too dry to kiss anyone. I might bother mentioning the reason to the guy or I might not... cause if your mouth is dry as a bone, you instinctively don't kiss as it's just not practical. Not really much of a conscious decision, and not an indication of how much I like the guy at all.
On another occasion my (now ex) bf and I, had been out to dinner and I was avoiding kissing him, and at the worst possible time. I could tell he was about to take it to heart... and had to tell him it was over garlic breath. It was easy for me to say it... as we'd both had the chicken kiev and were both in exactly the same boat. The next time we went out for dinner he asked me, completely forgetting about it "should we get a basket of the garlic bread?" and I said "Umm... maybe not". We had a good laugh (and didn't order it).
Anyway... could mean anything, could mean nothing. Personally, I wouldn't bail him up and ask him just yet. I'd prefer not to make a guy sweat the small stuff so early in the piece. I know communication is important, but I like to save the dreaded "I think we need to talk" for more important issues. Look at what he is communicating to you through other words and actions, and see if this kissing thing continues or was just a once off.
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