I don't think the DB punched it out, necessarily. But he did keep Romney from catching it on the rebound after bumbling the initial catch.

If Romney catches it clean to begin with, the DB has no shot at touching the ball - much less knocking it out.

But Romney bumbled the catch and the ball was loose - the DB hits the ball as Romney is trying to get ahold of it. If the DB wasn't there, there's a pretty good chance that Romney ends up catching the ball. As it was - the DB did just enough to keep Romney from gaining possession of a ball he should've caught cleanly the first time.