I looked at the post and really didn't get that impression. Sure, maybe it was a little "tongue in cheek," but ultimately the woman in the background has a great ass. It is a little funny that her ass is hanging out of her shorts, but the girl has got a fantastic backside. If you've got it, flaunt it, right?
Maybe he shouldn't have posted the picture, but I don't think he was shaming the woman. When you wear shorts like that, you want people to notice you. In this case, it happened to be a celebrity singer.
After the shit storm accusations of sexism and body shaming, Michael Buble issued an apology via his facebook page. What do you think? Did he deserve the ridicule? Should he have apologized?