I don't think a trade down from 21 is likely just based on parsing what Grier said in his PC.
Two things stood out to me.
One was that the team had less than 21 players with 1st round grades on their board but he expected a couple of them to be available at 21. I didn't get the impression he'd pass on those last couple of players with 1st round grades unless it was a deal that was too good to pass up. I think that would only happen if some team was desperate to trade up for a QB.
The second things was that when asked about a trade down, he answered as if it was only a consideration with pick 55. I think he really wants to add more picks in that 3rd-4th round range, but is only thinking about using 55 to accomplish that.