Why did he kiss me?

Did you slap him? Lol
Search your feelings: if you like him, you should be happy he made the first move

I would probably feel a little awkward and slightly emasculated.

But in terms of what you should do is probably get the hell away from this guy.
Hes probably made up so many fantasies about you that he now thinks your his girlfriend or something. Ballzy is usually good but not when its that ballzy. That would be considered sexual harassment in most books.

Only two options here:

A) You like him so you kiss him back and enjoy the ride :)

B) You don't like him, so you let him down easy. Tell him you don't see him that way and would like to be just friends.

Well if you like him. Kiss back. If you don't then go use mouthwash!