If TOGA thrust was inadvertently and unexpectedly applied, then the subsequent events have all the hallmarks of Somatogravic illusion. From:
Somatogravic Illusion - AviationKnowledge
...power is rapidly applied and the aircraft then accelerates rapidly ... As no visual cues exist, this generates a strong ‘tilt back’ sensation which the pilot interprets (incorrectly) as a rapid pitching up sensation. Despite this perception the aircraft may still actually be in a level attitude or only a slight climb ... This is the somatogravic illusion. The pilot will then push forward on the control column to control this (imaginary) climb thinking they are lowering the aircraft nose back to level flight, when in actual fact they are lowering the nose into a dive. As the aircraft nose lowers, the aircraft continues to accelerate, generating additional pitch up sensations, causing the pilot to lower the nose even further. Tragically, this illusion normal ends with the pilot commanding the aircraft into a high speed steep dive and contact with the ground quickly ensues.
Full Flight Simulators use this principle, except in reverse. Tilting of the simulator is used to simulate acceleration: tilt back = acceleration, tilt forward = deceleration.
If a rapid acceleration resulted in the F/O falling victim to this illusion, that would explain why he pushed full forward on the control column and also why he was unresponsive to the CPT's desperate attempts to get control of the aircraft. Having experienced this illusion once myself, I can tell you that it is overwhelming and results in almost total cognitive overload. The defence against it is awareness that it can happen and training in what to do if it does. In my training it was to 'Trust your Instruments'. ie Lock onto the AI and fly the attitude, regardless of what your body is screaming at you to do. And that struggle between doing what is right (fly the attitude) and what is wrong (push forward to counter the illusion) is all consuming - I doubt I would have been responsive to someone screaming at me either.