Fox just said the 3rd and 7 was his call, PM didn't audible into it. So we can put that to rest. Nevertheless, I thought they were too conservative on that series. If all you need is one 1st down, at least TRY to get it.
We saw the conservative method almost backfire a few games in the reg season where the opponent was given a last gasp, Denver had to recover a few onside kicks to keep the opponent from a last drive.