Hmm I'm wrong. Looking at rule book, Rashford wasn't technically interfering with play...
2. Offside offence
A player in an offside position at the moment the ball is played or touched* by a team-mate is only penalised on becoming involved in active play by:
- interfering with play by playing or touching a ball passed or touched by a team-mate or
- interfering with an opponent by:
- preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or
- challenging an opponent for the ball or
- clearly attempting to play a ball which is close when this action impacts on an opponent or
- making an obvious action which clearly impacts on the ability of an opponent to play the ball
The last one is the most applicable but he didn't actually take any action he was just there. Stupid rule