Disagree, if someone tugs at your arm i.e. a motion to pull down, then you do instinctively move your arm up then forwards to get them off. That is all that has happened, Robertson was just too close and too short and so it may have just accidentally caught his chin, but pure accident.
He got grabbed on the arm by a player ranting at him and just tried to shrug him off.
Robertson should be facing retrospective punishment given the HT whistle had gone and he was still remonstrating with officials. Despite all our shocking decisions on Saturday, officials still need respecting...