The player in that picture is not a QB. The player in that picture doesn't take snaps from the center, hand the ball off or throw.
What are you trying to say with that picture? How is it in any way relevant to a QB not being able to play if they can't grip and hold the ball with both hands?
I'm not knocking Carr for not playing. Its my opinion that he was encouraged to sit because we were already out of the playoff race, and the FO wanted to have an extended look at Rattler. Its my gut feeling.