From what I saw, one wrestler was far superior than the other. He probably had 10-15 moves that he could have used to put the other wrestler on his back. Why use this move, when he had so many more to choose from? Whether it was an illegal slam or not, I really don't know. Whether or not it was called for, I don't believe it was. If you are that much better than your opponent, just put them away and move on.