Having lost the IAS due to pitot they then did a zoom climb. This traded their velocity for altitude gain and resulted in the slower speed and stall problem. We can presume that the initial zoom climb was accidental as no additional thrust was applied, no announcement given.
For me this is the most puzzling part of the incident. Perhaps an accidental climb whilst trying to level wings in the chop. But +2500 feet? When instrument scanning you do your utmost to maintain them at the desired position. Corrections are done frequently and in very minor stick adjustments.
When they lost the IAS why did one of them not glance at the ground speed for a sanity check? You have it right there so why not.
They would have seen it change from >400kts to <50kts. C'est une grand problem, non? Perhaps the PAX seat back display would show ground speed change and they could even deduce a stall.
I say this not in cricticism of the pilots, but more as a question of what would I do if I lost my speed. Maintain attitude and power and treat her gentle as egg shells to buy time so my buddy can figure it out and call it in. Keep my scan going because that's all I have. No doubt it is more difficult because of the chop and warnings.
My gut say there is more to the puzzle. However I have a feeling we will never know. How do the more knowledgeable ones here feel about the PFD switch by the PNF and BEA want to record the instrument panel?
I was hoping to get an answer why the PF nosed up so radically. Reading the report 3 it looks like not yet, perhaps not ever.