The referee hasn't been overruled. He has stated he didn't see it and would have taken action if he did. That is the first stipulation of this type of FA charge.
A lot of people are talking like he's a loose cannon but if he has such a nasty streak, why has he only got 1 red card in 139 Football League games? https://www.transfermarkt.com/cameron-mcgeehan/detaillierteleistungsdaten/spieler/167265
Well done for pointing this out about just the one red card. There's not many stating he's a loose cannon, it was mainly the viewpoint of DWLC, one I disagree with. In fact I'd make Cam Vice-Captain to assist Davies out on the pitch.
Sam Hart!! His point of view is crucial to the outcome. Cam clearly apologized and shook hands with him straight after the incident, clearly confirming that he also thought it was accidental. if he is willing to bring that point of view into the hearing, Cam should be ok. I remember Kevin Betsy doing the same for a Colchester United defender, who was sent off for 'tripping' him. he gave evidence to the committee, saying that he had tripped on his own studs and the red card was overturned. Such is honesty. Let's hope Sam Hart is the same calibre.