Most Helpful Guy
I think this boy actually has developed feelings for you, and may have regretted rejecting you. And if he has started falling for you, well, his awkwardness would be self-explanatory.
A boy who is near an attractive girl or a girl he likes would feel nervous or shy. He may want to get her attention, but at the same time feel embarrassed or fearful he may mess up. A boy may want to leave a good impression on the girl or make a move, but being love-struck, shy, or fearful certainly doesn't help. (This is my personal explanation, I don't know if it's true or not. I'm no psychologist).
Do you still like this guy? Do you think he may be willing to tell you why he's feeling or doing what you observed?