"On seeing the UAS prompt......." The first input was NU, are you saying that was not an attempt to "SET PITCH" (at 5 degrees)?
The 5°/CLB thrust... memory items apply if "safe conduct of the flight is affected". Else the procedure is to "level off for troubleshooting".
"At STALL, the PF should have maintained ND". Not at all. He is trained to prevent loss of altitude. Cannot do that with maintained ND. The STALL warning is not STALL, something he has never experienced in this a/c.
I hope they weren't trained for NU inputs, as that obviously doesn't work all that well to prevent loss of altitude... Procedure at that time called for pitch reduction to 5°.
"augmented by manual nose down trim". NO. They were not in the correct LAW to have been prompted: "Use Manual Trim Only".
No, they just were not in a law that left them only manual trim, the wheel was still there to use. But why trim for nose down while pulling up?