1. There appears to be an assumption that Wilson was clearly offside. Freeze frame video shows this isn't necessarily the case. Or was certainly close enough to not have been seen:
2. LoTG page 180 says what to do in a goal/no goal situation:
When a goal has been scored and there is no doubt about the decision, the referee and assistant referee must make eye contact and the assistant referee must then move quickly 25–30 metres along the touchline towards the halfway line without raising the flag.
When a goal has been scored but the ball appears still to be in play, the assistant referee must first raise the flag to attract the referee’s attention then continue with the normal goal procedure of running quickly 25–30 metres along the touchline towards the halfway line.
On occasions when the whole of the ball does not cross the goal line and play continues as normal because a goal has not been scored, the referee must make eye contact with the assistant referee and if necessary give a discreet hand signal.
I've always believed in the event of a dubious goal the AR stays where he is, keeps his flag lowered, and makes eye contact with the ref. Remaining in position is signal enough that the ref needs to have a word. Though buzzers if available would obviously be used. Can't seem to find that in the book right now though.
3. When the AR raises his flag is he doing that because he thinks it's offside? Or because he wants a word with the ref?
4. I'm not sure it's clear what the conversation is about. Is the AR suggesting that Wilson was offside and asking Madley if he thought he interfered with play, as he wasn't sure he had? Is the AR suggesting that Wilson was offside and asking Madley if he saw him get a touch on the ball, because he wasn't sure he had? Or is he asking if Madley had seen a handball?
(Presumably the first two are possile, though not the latter - if Madley had seen a handball he would have given it himself.)
5. All in all, I think the right decision was made. If Wilson was offside, it was a matter of a centimetre or so of the toe of one boot. I don't think he impacted on the goalkeeper's ability to get the ball. And though there was a very slight glance off his arm, it: a) wasn't deliberate; and b) didn't divert the ball into the net, as that's where it was going anyway.
6. The only things I see wrong with the refs' actions were: 1. Madley took over 40 seconds from the scoring of the goal to get around to talking with his AR; 2. He made it very easy for lipreaders to work out what he was saying; 3. He had no control over the players or the situation (and employed some rather amusing and ineffectual whistle blowing, for no apparent reason); 4. Probably the AR would have been better off simply standing his ground rather than raising his flag. It's ambiguous, confusing, unnecessary, and escalates the situation from "I want a word before you give the goal" to "I think there's been an offence."