I find it very hard to believe that someone's arm could have been "jostled" to that extent - but what if one of the pilots (or the jump seat passenger) was out of their seat, and sudden turbulence knocked them off their feet and into the controls? It seems that an individual stumbling into the controls would be more likely to knock levers or other controls out of position, and if the individual landed in the PF's lap, maybe by the time that was sorted, the situation might have been unrecoverable?