It's my understanding the tube flipped over with the rider on it.
The rider was knocked unconscious, sank and drowned.
My assumption is that the vest actually came off.
The basis for my assumption is my own experience, in a major crash almost two years ago my vest came almost completely unzipped as I laid face-down unconscious in the water.
Are the new style competition vests safe enough?
As skiers, we generally don't like tubers because they mess up the water, but really most are just reckless and have no idea the danger that is posed when whipping someone (usually a child) at a high rate of speed.
Water skiing has inherent risk to it, but it's generally done in a controlled environment.
The contradiction of tubing is that while it's the easiest, it's likely to be the most dangerous.
Solution - take your kids kneeboarding.
You can still buy your 200k boat, but it's much safer.