My point about the autopilot is that the aircraft should have levelled off at the fcu selected altitude. The PF should have whizzed in a lower altitude, and then refined it second time around. Either way it should have been set at something above 100 or refined to 100 or msa. If the pilots were incapacitated then the ap would have levelled off at the fcu alt.
Who knows anyway, it's all speculation and the conviction here for this theory is unfounded.
There are many other possibilities. Some more likely than this one.