They still don't say how the ability to subvert a production container allowed the attacker to then subvert a fancy EIP-7702 MPC signature scheme that is supposed to depend on multiple parties (the whole idea being that if one party is breached the scheme remains trusted).

"the attacker logged onto Software Engineer C’s computer, used the credentials stolen from Wallet DevOps Engineer A, deployed a container, and triggered a malicious script to launch the attack."