My reading (having watched the MotD highlights) is that the lino saw both players in an offside position and instinctively raised his flag. The ref, seeing the flag go up had to double check because he was in a great position and saw that it was an Everton player who played the ball immediately...
He was already heading toward his lino before our players started remonstrating with him about the goal. He knew it was a good goal, and got that spot on.