They don’t add time on for set pieces though. Surely you know that? He Amy have been wrong not to blow before the pass, but he was still right to blow when he did.
Of course they do. If the ref adds two minutes and a goalkeeper spends one and a half minute to take a goal kick, do you really not think time should be added on?
Break-up of time added on:
45:00-45:24 - Ball in play
45:59-46:01 - Ball in play
46:31-46:34 - Ball in play
46:57-47:06 - Ball in play
Would you say that the two minutes lost to stoppages has been added back at the end of the period? Out of two minutes, the ball was in play for a grand total of 33 seconds. The ref then had the good taste to wait five seconds, not intend to blow when Maitland-Niles set himself up for the pass, but as soon as Martial broke he put his hand to his mouth to blow up.
I agree that he was technically within his rights to blow up at any point past 47:00, that much is obvious, but if the point of added time is to add time to play football, then he should've added more. It's just very suspicious that it looks like he's about to let WBA have another attack since he has no intention of blowing up when the ball's headed out to Maitland-Niles who sets himself up for a pass, but as soon as the counter's on he shits himself and blows his whistle.