This doesn't apply. This is when a player falls to the ground and the ball comes loose "AND THEN" the ball touches the ground before they've "caught" the ball. So you're falling, land on your back, ball pops out. The ball has to be loose before it makes contact with the ground - in which case it's an incomplete pass. However, if the receiver had possession of the football, the ball first makes contact with ground "and then" comes loose - it's a catch. Otherwise, if you applied this rule to all catches (which you have to correct?), then a RB that receives the ball in the backfield and runs for 50 yards before being tackled, however goes down and as he does the ball comes into contact with the ground and (while he still has possession) it comes loose...then the ball would be 50 yards back at the original line of scrimmage and ruled as incomplete (when it was clearly a complete pass).
The argument isn't whether it was complete/incomplete...it's whether he officially had possession before the ball hit the turf. That's why this rule specifies "in the process of completing a catch". That's the only time it applies. So was Enunwa in the process of completing the catch, or did he already have possession? I think he clearly did. So did the announcers.
The difference is where they were when they caught the ball. The rules are different if you catch the ball with your feet (or foot) on the ground vs. catch the ball while in the air. If you catch the ball while in the air, you have to maintain control all the way to the ground, whether that's just two feet or your whole body.
That's why your analogy with the RB running 50 yards doesn't apply. He either caught the ball with his feet on the ground or returned to the ground and began running while in control so it is a completed catch. If you catch it in the air, you have to maintain control through going to the ground with whatever body parts hit the ground in the time immediately following the catch. Just because your feet hit first doesn't "complete the catch" if the rest of your body goes to the ground immediately afterwards.