Not reel sure as to what a blowout is on said boat ?
Boils down to the prop losing bite in the water, whether it be due to running in shallow water, something hitting the prop or wrong lower for the speeds being ran, which causes water to be diverted from the prop at high speeds or by over trimming. Sometimes it will create a "bubble" around the prop and causing you to lose steering capability, cause the prop to feel like it is in neutral and the tachometer to rise while the nose of the boat goes down. All this happens in a few seconds and can cause what you just saw. Experience and caution can avoid this type of accident. Apparently these 2 guys had neither.