I don't know about the whole frat and soror thing but I have the same questions. But I do know this that my girls mostly want to be deltas and my boys are mostly Kappas. I think its because of the red and white thing reminds you so much of a candy cane that there always the first ones to strike to your head.
Did he mention why he wasn't in a frat? I would have been interest in hearing why or why not he would join.