Quoting RWA:
...if they'd wound the trimwheel forward to reduce the huge (13-degree) 'up' angle the systems appear to have imposed, the autotrim would presumably just have wound it back to 'Square Thirteen' again
The systems only imposed the 13 degree up angle because the pilot asked for it by backwards pressure on the SS that increased the pitch angle to the point where the aircraft stalled - the system was doing exactly what the pilot requested. Even then, if he'd moved the SS forwards again to try to reduce the pitch angle (and consequently the AOA), as you'd expect any pilot to do when in a stall, the system would've moved the THS accordingly.