This is sounds very similar to the Kenyan Airlines crash. If my memory serves me correct the autopilot on the NG cannot be engaged while force is being exerted on the control column.
Possible senario: PF calls for A/P, PNF reaches over press a/p, p/f sees this confirms a/p whilst hand flying and without checking FMA (a/p has not engaged). PF let's go of controls.
Sound far fetched?
Seen it happen more than once.
Assy