I realize that the resultant tail-wagging could have been misidentified, just adding to the confusion, but surely, most competent PNFs, would have an awareness of the actual pedal movement. Perhaps it's ‘bad form' for a young co-pilot to hover over the captain's controls, but as a captain in these conditions, I know I would have had a tactile awareness of the pedals. Under the circumstances, it sounds as though it would have been difficult not to have. Perhaps by the time it was clear to the captain, it was too late.
They had a sudden, violent and totally unexpected wake encounter at an early stage. Not sure how flap retraction was going and the distraction of the After Take-off checklist. With the sudden buffeting, I think it is understandable the Captain was more pre-occupied with what was going on with the aeroplane and whether the co-pilot was coping- hence the query. I am sure no attention was given to the rudder pedal movement for those seconds, and indeed the violent movement of the rudder pedals (obscured behind the control column and his knees) was not noticed- any pilot had he seen that degree of movement would have queried it out of concern- and in the buffeting probably the motion induced by rudder overcontrol would be masked by the turbulence. I do not believe any pilot can identify yaw in different directions and apply full control and then reverse it at that rate, then repeatedly carry it all out again. Sadly, we do nobody any service by denying the obvious- the fin came off because of violent and sustained overcontrol. The way ahead is to ensure all pilots are thoroughly educated on limitations of the system, much as we have been educated on likely causes of 737 rudder hardovers and how to handle them.