Can't help but wonder if he would have given it if he realized it was the second . . . looked like he got good help through the earpiece on not noticinig it was 2C and figuring out if the sub could come on.
I'm more impressed by the commentators for being able to figure out exactly what was going on while it was going on. Can you imagine if this happened in an MLS game? They'd be absolutely baffled, and probably moan the rest of the match that the referee had made a mistake by not allowing the substitution.
This is leaving me confused - what exactly is going on in this whole affair. The extra step from the touch is worth a sending off???
His behaviour (the mock applause etc) towards the fans as he leaves the field is USB in the referee's eyes. So he cautions him, then realizes he already had one, sends him off, and clarifies that the caution-worthy act took place before the substitution was completed, so therefore the substitute had to stay off (although he had already run on since). There's nothing wrong with it in law.
This is what the referee was going for. Looks great when he's not already on a yellow. Costs you nothing, and you really seize control of things.
The exiting player was cautioned for how he left the field. (And a teammate is cuationed for protesting, but that is irrelevant.) R then realizes (players are telling him and he probably hears it from an AR or 4th O) that it was a second caution. So that makes a send off. Since the caution was for behavior before the sub was complete, the departing player was still a player -- so he can't have a sub. So the sub has to go back out -- the sub was not cautioned/sent off, but was unable to enter because the player he was coming in for was sent off before the sub took place.