When a guy smiles to himself?

there's this guy that I keep seeing around and he's smiling when he sees me from far away but when is close doesn't, recently we were walking past each other and he was really close he didn't look up at me but noticed that I was there he looked at my bottom half (I mean he saw me but didn't make eye contact) and smiled really widely to himself?
Updates
+1 y
thanks for your reply, I have never spoken to him. he's always with his guy mate so makes it harder. there's loads of other pretty girls in the class but I never see him looking at them, I wouldn't believe he could be shy he seems reserved but confident, if he's doing it in the jerk way then that would totally put me off
When a guy smiles to himself?
Post Opinion