There is no special need to protect the head from getting slammed in an avalanche. What the bag does is that it protects you from being buried and crushed beneath a ton of snow. Both by making you "float" higher when caught in the avalanche. But also by taking up space when buried, so that when it deflates you're in a "pocket" and not getting crushed.

Haven't seen the video before. But In often see racers being "bulky" when skiing down after an accident. Looks funny, but it's useful.