Random guess at whats happened here...And it follows the same mindset, in reverse, of the diabolical non awarding of the Sheff goal the other week...
Ref might well be watching play, he might well be pretty sure the defenders played it, but
The attacker is certainly in an offside position, the AR has buzzed, flagged, and prob shouted " offside" over the comms, so, bit like the Sheff AR in reverse, the ref here has everything bar his own thoughts telling him, offside.
Fearful of a collision between attacker and gk and then an offside restart, he has conformed to instinct, and stopped the game.
am also so so on the need to actually wave the flag down here, the flag in an offside situation provides one purpose....to inform the referee that in the opinion of the AR someone is in an offside position and should be penalised.
In this clip, imo, an extra hand signal from ref was not needed, the referee should have ignored AR and let play continue, by all means when goal scored, go for a chat
also from the clip, the ref is nearly at the AR yet taps ear to indicate to players he is talking to the AR, use some common sense and actually talk to him for real, the stadiums empty, he is only a few yards away and all you need to know is, " are you flagging offside from the through ball"
restarting with the offside is beyond schoolboy material, its what a new grass roots ref would do if they had a brain fart during a game.....it be understandable at park level but unnacceptable from a fifa referee.