Firstly, hello! from a newbie. I have been following this thread with interest as a controls engineer, but in the automotive world rather than aero (more 2d than 3d, but many more things to hit.......)
So, please forgive me if this is made up rubbish, but:
assumption 1) no spatial awareness by the pilots (nighttime, possbly in turbulence etc)
assumption 2) they are aware of unreliable airspeed and possibly other instrumentation faults
assumption 3) They have no reference to quickly decide if the stall warning gongs are valid, or just due to unreliable airspeed
assumption 4) they have no way of knowing that in fact, the aircraft has not suffered some major structural or systems failure
assumption 5) Scaning the flight displays, the one number that might stand out, would be the altimeter winding down at a massive rate, and maybe with other signals, such as cabin pressure changes, and possible abnormal wind noise etc (due to the extreme AOA), helping push that "fact" as "True"
assumption 6) Without other stimulus, i could see how one could assume that in order to be loosing 10k f/min altitude, the plane "must" be in a steep dive (negative pitch, nose down) (I'm not sure if the thought of a "deep stall" would have even occured?, esp in an aircraft that is "impossible to stall" (not true obviously, but i can again imagine that after 10k hrs stick time, you might formed an option of the aircrafts correct and accurate control response to most unusual situations
assumption 7) Pilots cannot trust the autopilot with degraded information (i.e. the phantom steep dive "could" have been caused by the automatic flight controls pushing the nose down to maintain speed, except the pilots know they can't trust that speed, so by default, the actions of the autopilot might not be trusted either)
I these cases (and i admit it is a complex series of scenarios) then throttling back, and pulling "up" could possibly seem like a valid response. (especially if the lack of pitch authority might have seemed like the result of a mechanical systems failure (instead of the deep stall) ??
Unfortunately, in the limited time availible, they were unable to work out what was actually happening to the aircraft. (it would be a brave move to go full throttle and stick forward if you genuinely "believed" you were in a steep fast dive would it not)
Appologies for the lack of technical jargon, but if you assume that the pilots were trying to "pull up" the entire time, then something must have caused them to carry out that action?