Hi DozyWannabe,
Not to mention that the autotrim does not and did not move of its own volition
autotrim will move the stabiliser without any input from PF. If the speed of the aircraft changes, then the trim will run to help the elevator.
Once PF had commanded a pitch attitude which resulted in a real (not just spuriously indicated) speed decay - even if he didn't touch the side stick again - the FBW computers would attempt to maintain that trajectory by moving the elevators and hence the stab trim.