It's too bad and people make mistakes. Sometimes we don't get to walk away from them. But of the spotty information I read and heard, the thing that doesn't make sense to me is that the survivor mentioned they were "anchored when the boat flipped and they all had life vests on." Yet no life vests were found. They found a cooler and other debris some 16 miles from the boat. Even if they were taken by sharks, I would think at least parts of vests would be found. They don't sink too well.
Without vests, panic alone kills a lot of folks in this type of situation. A couple good gulps of water, they panic, and that's it. Clothes and shoes make it worse.