So, assuming the captain had side-stick priority, then any inputs by the co-pilot would have been ignored, as the jammed camera was making a constant input on the captain's side-stick. If the co-pilot had pushed his own side-stick priority button, then he would have been able to pull the A/C out of the dive, allowing the captain to retract his seat and cease the input on his side-stick.
From what I read in the report, that's exactly what they did, but by then the aircraft was already recovering itself. The captain was convinced autopilot was engaged and diving the aircraft, despite the visual and aural indications otherwise. Because he couldn't pull the stick back due to the then-unseen obstruction, he gave a clear instruction to the co-pilot to take priority and disengage AP. At least that was my interpretation of it.