'if HAL was reacting to the overspeed warning and the reversion to control law "x"'
From the report.......(edited down)
At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight. The PF continued to make nose-up inputs.
Is there any need to postulate a malign machine ?
Also, once in the descent with ROD constant, it would have felt like 1g through the seat of your pants. If the ROD increased with ND input, the sudden resurrection of the stall warner plus the feeling of lightness can't have helped convince that was the right thing to do.