I've worked with and around snowboarding and pro snowboarders for most of my life. This stuff always shakes people up when it happens, but honestly, dudes don't even really think about it on a day to day basis. These guys are so good that it just feels second nature, although most are pretty conscious of their limits, and don't just do something crazy and out of their league on a whim. Now, I can't speak for this Caleb dude cause snowmobilers are a whole different breed, but the trick he was doing was one that I'm sure he had done 100x before and one that he worked himself up to learning other things.
Two things I can say though... First, the whole "extreme" vibe doesn't exist with real snowboarders. Most will laugh at you if you even say the word cause its kind of a douchebaggy notion. It's just what they love to do, and some of them are really good at it. They're not out there to "push the limits of the human body, man." That's what guys in Mountain Dew commercials do.
Second, one area where nearly all these guys are extremely cautious about safety is around avalanches. You just don't mess around there. I lost a good friend in an avalanche last year and its pretty devastating when it happens.
But as far as serious accidents in contests like these, they are really rare. I actually feel like I see more injuries in the NBA than I ever have around snowboarders. Lotta bumps and bruises, but the serious or fatal injury is rare, at least in my experience, but when it does its really scary. I didn't know him personally, but a bunch of guys I know were close with that guy Kevin Pearce who suffered a serious brain injury during Olympic half pipe qualification circuit. He pulled through, but it was scary.
Also side note... Most pro snowboarders think the x games are stupid, just like most contests. Half pipe guys love em, but its kind of a thing you just do to put some cash in your pocket for most people, and then you go travel to ride for real.