It's just him being affectionate. I don't think you should interpret too much into it...
It means he's taller than you :-)
It also means he's fond of you, but that could be as just a friend. I wouldn't read any more into it unless you have other reasons to think he is romantically interested.
A kiss on the head can mean something more than just being an affectionate friend. That being said you shouldn't put too much into it. If there is a bigger meaning behind the kiss than just being friends then there will be other signs.