Gun damaged, or just a case head let go? It's not clear from your description. Other than a mag being damaged or grip panels cracking, it seems unlikely that a case head letting go would hurt the gun much. Small advantage of a steel frame, over plastic 
I'd guess:
1. Overpressure
2. Too-generous chamber dimensions
3. Combination of #1 and #2.
That pretty well ought to cover it. If it was a plugged bore, you'd be picking pieces of barrel out of the shooter's face, not brass. Shooter error seems unlikely?
Case heads do let go, that's why we wear safety glasses.
Send the ammo back.
I'd guess:
1. Overpressure
2. Too-generous chamber dimensions
3. Combination of #1 and #2.
That pretty well ought to cover it. If it was a plugged bore, you'd be picking pieces of barrel out of the shooter's face, not brass. Shooter error seems unlikely?
Case heads do let go, that's why we wear safety glasses.
Send the ammo back.