But he didn't stay out of bounds and he did influence the play, he just failed to return at the first opportunity. Had he stayed out of bounds and not participated, there would be nothing here. He gained advantage (and I am introducing new details here) by bypassing R players in the field of play as he ran out of bounds, and only returned at the spot of the ball at rest. As soon as he pounced on the ball, he was participating again, and given that he did not return at the earliest opportunity, that now becomes illegal participation.
I wish I could share video of the play in question, I think it would be easier to see it than go off of my sparse description.