Other than airspeed, which he has reason not to trust; angle of attack, which isn't displayed?; and an aural stall warning, which is apparently inhibited, how else does he know that he's stalled?
That is the bit that seems to have got them totally confused.
The AoA vane plus IAS provides the stall warning. Only problem is that the IAS must be greater than 60KTS for the combo to provide the SW. The SW stopped because the IAS had dropped too low, and when they attempted nose-down and got an IAS over 60KTS, the SW started again.
Their logic told them it was the wrong thing to do, hence the persistence with nose-up on the side-stick. I wonder if the actual AoA had been available, what they would have made of it?