On a fumble, that's the rule. If the player contacts the ground, and that contact causes the fumble, it's not a fumble. But on a catch, the player MUST maintain complete possession until his body stops moving, after impacting the ground. So it doesn't matter, according to this rule, that Holt caught and secured the ball. Once it pops out, it's an incompletion.
What's stupid about that is, with that exact same grip Holt could have run for 80 yards. Had he not caught it diving out the back of the end zone, it would have been a completion.
If the ground can't cause a fumble while running, it shouldn't cause an incompletion, either. Holt clearly received the ball and tucked it, but that's not good enough for this rule.
There are situations where this rule has an application. This shouldn't be one of them.