Yes, it's her workplace, but I think that's irrelevant. It's also a public thoroughfare, and what the guy did can probably be construed as simple assault. A slap in the face would certainly be simple assault; I don't see how a slap on the butt is anything other than that.
My problem is with statements like "He took my power." No he did not. He slapped your butt. You maintained your professionalism instead of dropping your professionalism and getting angry. Getting angry, shouting something at him, would have been an entirely reasonable response--but I see why you didn't do that. Still, the appropriate nonprofessional response would have been something like "Hey a&&hoLe, keep your hands to yourself!"
Borderline whining on CBS This Morning, however, and saying, "He took my power," is just silly.
It sounds as though he's apologized, and of course his life has been ruined for the moment. So the karmic wheel has taken care of him.