"At a height of 900 m there was a simultaneous control column nose down input and stabilizer 5-degree nose down deflection.."
The control column nose down is a PF commanded input. It is the STS that is of particular interest in this scenario where the aircraft was on manual, ie a/p disengaged. STS most frequently operates on t/o, climb and go around.
The puzzling of the STS against the background of the investigators announcement that no systems faults have been found, is the word "simultaneous". Namely that both commanded input and stab deflection occurred at the same time. Cannot quite see how both could have been achieved simultaneously.