From my rough understanding, this seems like the main exploit. It seems like the machine with access to the wallet key was presented with a crazy EIP-7702 transaction and signed it (which effectively owned its wallet in a single transaction)[1]. Without knowing their security model, it seems like biggest trust boundary should be between that signing machine and everything else.

[1] The fact that the needed to sign 50 of these transactions to solve a race condition seems like an implementation detail