The pilots were not making an 'absurd error'. They did not forget to fly the plane.
It is that what they thought they were doing was not what they were actually doing. Their mental model broke away from the reality. (They thought the plane was in 'normal mode' when it was actually in 'abnormal mode' -- an expression of which: one them declaring "this cannot be happening!")
Telling them just fly the airplane is not (quite) the solution -- they thought they were flying it.
But the remedy is sort-of basically correct. It just seems better expressed as: when nothing makes sense (your mental model has suddenly utterly failed), fall back to a more basic backup mental model and system -- like primitive manual override.
(How clear can such separation of a basic mode be? How practical would it be? How reliable? It leads to a set of engineering/UI questions . . . were they well designed in this particular case?)