If we are being pedantic…
When he receives the ball he has the opportunity to be one on one, or alternatively he is in a position to be one on one, is that better?
The flag/whistle was pretty much immediate, it went just around the time he touched the ball. A half second later he is half-battling for it, and then the game stops.
What happened after the ball comes through, or after the flag goes up, is irrelevant in context of the actual decision itself.
It was a scandalous decision, and I don’t understand anyone defending it.