Did he shut off your primary and secondary regulators at the same time?
Just the primary. You knew when you were suddenly OOA that it was a drill and you had to go to your buddy, not your alternate.
Now, there was a time he shut off my alternate. Of course, I could not tell he had done that. Then he put my buddy OOA. I donated, picked up my alternate, and had nothing. He was simulating a left post roll off, which can happen in a cave or wreck. In that case, I just reached back and turned it back on.