I think it was offside, but RM should have been given a penalty in the first half. I am aware the game shouldn't be examined that way, but in a vacuum of this game, it can be viewed as a balance.
RM also got the favor in every off the ball collision and a few ignored calls today for Betis (like a handball from Isco earlier). For all minor incidents that disrupt Betis or facilitate RM, you guys get the ref's help.