A loop is a cheap and easy thing to do. With the wheels spinning, I wonder why it broke, was it just that much more power instantly put to it or was there a mis-alignment issue?

What continually amazes me are the knuckleheads in the crowd... all crammed in close and "on axis" with all the spinny parts - like u-joints, clutches, flywheels, etc.
Doesn't matter how many sit-ups you do in the morning, having a u-joint cup in your spleen will ruin your day!

John, that’s exactly what I thought the instant I saw the video.
Two theory’s might apply here, the Darwin theory and God looks out for idiots. See any hold back straps? Think anyone inspected the dynamic components prior to testing them to their maximum load.
Looks like the driveshaft failed close to the mid section; I think I would suspect balancing or misalignment.