Here's the rule. Apparently Likely failed to complete the "additional step" referenced below. I still question why that should be required in the end zone.
Let's say a guy catches the ball with two feet in the end zone and, without moving either foot, spikes the ball. Nobody would rule that an incomplete pass.
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, clearly performs any act common to the game (e.g., extend the ball forward, take an
additional step, tuck the ball away and turn upfield, or avoid or ward off an opponent), or he maintains control of the ball long
enough to do so.