First off, Lion fish are devasting reef fish populations, and this guy is absolutely doing excellent conservation work by offing as many as he can. I've heard of attempts to get local shark populations turned onto the taste of lion fishes by spearing them and then feeding them to certain species of reef shark, which apparently can digest them without incident. (This may lead to future encounters with spear fishermen, but also fewer invasive Lion fishes...)
Second, as others stated, Lion fish are delicious.
Finally, if a shark is trying to steal some tasty, bloody fish from you, I'd generally recommend hunkering down, as opposed to free swimming to the surface.