What went wrong here?

User error.

He wasn’t vaccinated.

The cylinder wasn't completely closed so the bullet shot right into the frame making the gun explode. This is why you don't spin and flick close the cylinder because it can become off center and cause this problem.

Clearly, his palms were sweaty. Knees weak are were heavy

It appears the gun broke. Glad I could help.

The safety was obviously still on.

Anti-theft device?

Barrel obstruction or too hot handload. Look at the muzzle flash and recoil. The flash is below the barrel, and the recoil is light. The bullet did not leave the barrel.

The consensus in my house is they are using the wrong ammo. Something that that revolver can’t handle. That kid is lucky he didn’t get hurt.

Its a Dan Wesson with interchangeable barrels. Barrel was not tightened to spec. Its why DW kept getting sued into bankruptcy.