Isn't the rule the ground can't cause a fumble? I think it was a first down unless they changed the rules.
It was a blown call, but the ground CAN cause a fumble if the runner is not down. A runner is not down until a body part other than a foot or hand touches the ground. They had to determine if Gio's forearm was down before the ball was dislodged after the back of his hand hit the ground. If Gio lost control of the ball when the back of his hand hit the ground while his forearm was still in the air, it was a fumble. His forearm was clearly down in my opinion. Their inability to determine that was the reason why "the play stands as call" rather than CONFIRMED or OVERRULED.