PF was confronted with a situation that he was not trained for i.e. UAS at high altitude.
I think this is too charitable. The one thing that we know they knew is that they were descending very rapidly. Aerodynamically, there are two ways for this to be the case: (a) they were in a deep (and fast) head-first dive; or (b) they were in a full tail-first stall. [Note, I am excluding the situation of the plane being fully laid over on its side.] Is it possible that things were so upset in the cockpit that over the course of three minutes in this attitude they were unable to discern the 60+ degrees of pitch difference between (a) and (b) -- and to remain convinced that it could only be (a)? I guess "yes," because the computer game stall warning was "god," aerodynamics be damned.