Previously, when the ball is passed to a player in an offside position, and he knows he is offside, we've seen that player stop moving, or move away from the ball and put his arms in the air to tell the ref, "I'm not interfering". What happened today has changed all that and set a new precedent - the player can now follow the ball, without touching it and be deemed to be not offside.
if Rashford stops running, there is no way Bruno get nears the ball and both city defenders and keeper would clear the ball, the fact Rashford keeps running towards the ball makes both city defenders and the keeper to act, so Rashford is interfering with play,
also the linesman should be flagging early like he did for the city players in the game, Foden a couple of times was clear and a early flag was waved stopping the play, it's shocking and a gift that will get rewarded in a brown paper bag