It was indeed a great dunk. BUT I don't see it as dunking "over" the defender. In my opinion a player who is dunked "over" jumps , arms extended, trying to block the dunk. But, is unsuccessful.
The defender played the situation well! He was just a help defender coming from the other side. He was not in position to play the ball. He squared his feet, outside the semi circle, to take a charge. Two seasons ago it would have been a charging call. Now it should be a "no call."