I doubt its anything like that. What is most likely is that they cloned(Nand Cloned?) the entire contents of the phone and emulated it in a virtual machine. They try 10 tries at the pin, if it bricks, they kill the virtual machine and spawn a new one. Rinse, repeat until they get a valid pin.
Clearly it takes some pretty sophisticated techniques to accomplish this but it's faster than trying to brute force a 256bit key, which it's essentially impossible as we know it today.
Might be a novel way - create ‘billions’ of virtual machines and brute force them. You don’t need to copy the data, just enough of the OS and the keystore ... until one opens. Create and discard in a ‘wave’ as they brick, freeing up prior disk space and processor power.
Finally you guess right ad win the PowerBall.
Probably could be done on a few terabytes of fast solid state disk space and an obscene amount of RAM.
Clever.
I like the way you think ...