He clearly moves toward the ball. He pretty much dummies it. He's also in everyone's sight lines. If that play is not offside, there are 3-4 incorrect offside calls per game. They would pretty much have to wait and see if the player plays the ball before blowing the whistle.
That's what referees have to do. Wait to see if he plays or attempts to play the ball. That's the law.
It may also be affected by whether or not we get the benefit of the doubt in at least one key decision in the second half. All such decisions have gone to the home side so far.