He saw you scratching your balls and didn't want to touch your hand.
Maybe he passed you in the bathroom and you didn't wash your hands.
Maybe your buddies told him that you have a horrible hand disease that can only be passed on by shaking hands.
Maybe he didn't see you offer the handshake or was already committed to the hug and didn't want to get caught in that ridiculous moment where two people can't decide if they are shaking hands or doing some ghetto hand slapping.

In any case, it's certainly nothing to worry about. Unless of course its one of the first two, in which case you have horrible hygiene. ; )