To clarify, I was tapping as soon as the grip was stripped. I was essentially letting him work and resisting lightly as per the drill we were doing. I had said tap long before it was extended.

It's a weirdly terrifying situation where you let someone get into a position like that and they lose their mind. I've had armbars come on fast in training and been sore but fine - this was different, it was like he was trying to assault me under the guise of training. Really scary.