Who knows dude, but think about it. Knowing that you're on LIVE TV -- I mean it sounds like she was holding in some crying or screaming to keep as much composure as she possibly could. No one wants to make a fool out of themselves on live television, and her body was doing the best it could while she was in excrushiating pain. I'd like to see what happens to someone that finds this funny if that ever happened to them.
Or how would you like to be on tape while one of your "friends" shot at you? Knowing there was nothing you could really do because you were standing on a rock in the water that was quite a long distance from the shooter? And oh yeah, there's a camera on you. Again, you wanna keep as much composure as possible while on a camera... he probably held back as much as he could, but there's some things that just come naturally that you can't hold in any longer. It's no different than the idea that someone who holds in their problems longer than someone who doesn't has a hard time (or looks like a fool) when showing their true emotions.
I'm not saying the kid wouldn't have had a hissy fit if he wasn't getting taped, but regardless, I'm sure him KNOWING that it was being taped made him feel even more helpless. When you feel helpless and you're getting attacked, you're going to get even more pissed.
Talk to any psychologist about this. Our society is hooked on accidents in reality television/websites and can't even understand why it's so much worse than usual...