I've watched it... and I've decided for myself. This isn't what it seems to be. For one, the angle is quite convenient for such an accusation. It shows two things lined up with motion. But, it doesn't show any contact, therefore any conclusions are just assumptions. But also, watch the relative position of his right elbow in relation to his back, both before and after he removes his hand from his coat pocket. Both before and after, his elbow is clearly behind his back. (Meaning, his arm is rotated slightly backwards at the shoulder.) It's pretty hard to reach out and slap someone's rear end while keeping your elbow behind you. Try it, you'll see.