Just watched the play again and it still looks to me like Humphrey puts his arms around Scott before Scott can even initiate anything. At most, you could say it was a bang-bang play that wasn't conclusive enough for the ref to call.
Come to think of it, even if there was a "pick," it still would have been legal. You're allowed to set a pick on the defender who's covering you, as Scott was intending to do. Where it becomes illegal is when you set a pick on a DB who isn't covering you in order to free up a teammate. But that's not what happened on that play. Renfrow was wide open because Humphrey yanked Scott to the ground and forced Brown to go around them, not because anyone made contact with Brown (which they didn't).