The "Russian Translation" if accurate implies the stabiliser was running away, either uncommanded or by human intervention Aka all the theories voiced herein. Something about a " fin switch" can only relate to the stab trim cut outs by the throttle quadrant, part of the memory items, or the black guarded cut out switch at the rear of the pedestal used by engineers ( clutch). I agree if I was flying and the other person was trimming down I would quickly notice this and firmly holding the column would stop this, so thats more than confusing to say the least. Runaway stabiliser is trained in the sim and unless the crew were operating with opposed opinions of the events it should be manageable. Its conceivable that with fatigue and hand over of controls for weather conditions a complete lack of SA occurred, sadly.