In my opinion, pulling his pass is very harsh especially you did not know what happened to the young man before he fell on his butt. It could be that he accidentally slipped on ice. It could be that he was trying very hard to avoid another person that ran into his way from a blind spot. He was out of control after he fell on his butt (of course. I don't think anyone can be in control after fall on his/her butt), but my guess is that you have no idea whether he was in control before since you did not see whatever happened before. So no, with the amount of information you provided me, I don't think you accurately judged whether he was in control or not. Accident happens. And if it is predictable, then it would not be an accident. You could be very well in control at this moment and not in the next second. Unless he was truly out of his mind, I don't think he wants to run into any of you.
I'll just make another example. Person A is cruising on the highway at 65 mph. And suddenly the truck in front of him brakes really hard. Person A swiveled to avoid the truck, drifted around the truck and narrowly misses a vehicle stopped on the shoulder. Question, was person A driving recklessly and out of control?
You're mistaken. Very mistaken. He was out of control at a critical point. I've skied a long time. If I lost it and nearly ran over a wreck site, I'd full well expect my pass to be pulled. Matter of fact, if I did, I'm confident that I'd be fired as well.