That's the old "going to the ground" rule that still exists on the books in a different form (i.e., not taking precedence over the main catch rule like it did in Dez' case)
RULE 8
ARTICLE 3. COMPLETED OR INTERCEPTED PASS. A player who makes a catch may advance the ball. A forward pass is
complete (by the offense) or intercepted (by the defense) in the field of play, at the sideline, or in the end zone if a player, who is
inbounds:
(a) secures control of the ball in his hands or arms prior to the ball touching the ground; and
(b) touches the ground inbounds with both feet or with any part of his body other than his hands; and
(c) after (a) and (b) have been fulfilled, performs any act common to the game (e.g., tuck the ball away, extend it forward, take
an additional step, turn upfield, or avoid or ward off an opponent), or he maintains control of the ball long enough to do so.
Notes:
(1) Movement of the ball does not automatically result in loss of control.
(2) If a player, who satisfied (a) and (b), but has not satisfied (c), contacts the ground and loses control of the ball, it is an
incomplete pass if the ball hits the ground before he regains control, or if he regains control out of bounds.
(3) A receiver is considered a player in a defenseless posture (See Rule 12, Section 2, Article 9) throughout the entire
process of the catch and until the player is capable of avoiding or warding off the impending contact of an opponent.
(4) If a pass is caught simultaneously by two eligible opponents, and both players retain it, the ball belongs to the passers.
It is not a simultaneous catch if a player gains control first and an opponent subsequently gains joint control. If the ball is
muffed after simultaneous touching by two such players, all the players of the passing team become eligible to catch the
loose ball.
(5) If a player, who is in possession of the ball, is held up and carried out of bounds by an opponent before both feet or any
part of his body other than his hands touches the ground inbounds, it is a completed or intercepted pass. It is not
necessary for the player to maintain control of the ball when he lands out of bounds.
.