On the contrary, that receiver damage is entirely consistent with firing out of battery. The unsupported case head blew off, releasing high pressure gas into the action. The bolt was partially locked, just enough that the left bolt lug failed, causing the action to twist, cracking the receiver ring.
Rapid bolt movement in a slamfire situation might or might not crack the receiver heel, depending on how much partial bolt lug engagement slowed the bolt.
High pressure failure in an M1 rifle acts quite differently.
Just about as credible an answer and theory as you gave in the other thread, on how it could not possibly be an out of battery slamfire.
Still waiting for your expert answer on whether the age of ammunition matters and whether previous storage conditions, matter.