He was probably trying to be seductive. You will often see in movies a woman who being seductive will lick her lips. I'm guessing he either had something on his lips that he wanted to remove (like food) or he was trying to be seductive. LOL
*other* than the guy likes you? eh, seriously, I'd need to see it to know the context better. Please don't tell me it was a really ham-handed effort at flirting. Otherwise, it's just subconscious, and I doubt he could even tell you. If you had a good conversation after, what does it matter?
maybe it's his nervous tick - he was probably nervous/concentrating/anxious.
Well, it could have been that it was a forced kind of licking lips. Or it could have been just his subconscious. Maybe he was licking his lips to prepare for conversation. Maybe it was because he likes you, maybe it was because he wanted to kiss you.