Autotrim did not put the aircraft in unrecoverable stall, the PIC did by continuing to pull up
The point is that without autotrim, the stall would have been less severe, the pilot might have been able to recover or the nose might have dropped on its own.
Also, if I understand correctly, autotrim was NOT supposed to work this way. If the system knew the correct speed, trimming up would have been inhibited. In this case, speed was unknown and AOA/stall warning not taken into account by the system logic...