It was skill because it's something he trained. But you still have to be very lucky to land it. Overemphasized by the fact that yair was losing the fight and could only win with a ko or sub and it happened with seconds left that KZ could have just defended. But he instead got lured by yair into putting on a show for the fans, by brawling, when really yair wanted to brawl so he had a shot at a ko knowing he would lose otherwise. It was definately KZ fault, but I honestly dont remember seeing yair throw it on any other occasions or the announcers mentioning him throwing it.