I'm not sure why he died since it wasn't that great a height, onto soft surface, and he landed on his feet - broken neck? But die he did - or does, on-vid.
It is certainly an unexpected conclusion to what looked like a harmless jump. No doubt everyone involved was duly surprised. I'll bet whichever kid was next in line to make that leap changed his mind.
Do you have any evidence for that? I agree it's very unexpected, but I looked at it very carefully twice for just that reason and it looks very convincing to me.
Sometimes it's impossible to tell - different people who all know enough to have a worthwhile opinion come to different conclusions, and there's really no way of knowing which is right. I have neck problem, and if I did that jump I'm not at all sure I'd survive. But actually that is a pretty major impact passing up through his body, same range I'd guess as a long-drop hanging. So if it caught his neck at a bad angle or he had any weakness there, it wouldn't surprise me at all if he died. And that's rather the way it looks to me - he seems ok for a moment until the shockwave reached his neck, then suddenly ...