KBarret is right, either this was a round loaded with pistol powder (unlikely), or it was an out of battery ignition.
From the pictures it is clear that the failure initiated in the barrel extension; which means the likliehood of a squib induced catastrophic failure is very low.
Because the bolt head and barrel extension are not sheared off, it is also very unlikely that this was a failure caused by a charge of a very fast powder (like a pistol or shotgun powder); and the .223 case doesnt have enough capacity for a max fill charge to do this (generally speaking a max fill overcharge of a very fast rifle powder in .223 will result in a case head separation at worst).
From the damage, the fact that the bolt head wasn't sheared, that the barrel wasn't banana peeled, and that the barrel extension was the clear initiation point, this really can only be an out of battery ignition.
Now, this could be the fault of the ammunition; but I don't think it is, at least not directly. I think you had a sticky round slamfire. The round didn't chamber completely, but the firing pin had enough energy to ignite a slightly softer than normal or more sensitive than normal primer.
I'd be willing to bet that if you had chambered some of this ammo, then cleared the chamber and checked the primers, you would have seen a slight firing pin impression.
This is why military 5.56 is loaded with special very hard, and less sensitive primers; and why full auto (and many semi-auto but not all) AR platform guns have a lightened firing pin.