This is just out of curiosity, if Federer sat on Nole's chair by mistake, then why didn't he move to the other bench he was initially assigned to, once he realized - assuming he did at one point as they had to move Nole's stuff?
Also, isn't he a professional to know this anyway unless you say he's finally getting old and alzheimer is probably kicking in lol (I kid) and was in this situation many times before. How could he possibly make this mistake given all that?