It is anything a runner would do to avoid defenders and/or advance the ball. It is the intent to do something that is not part of catching a pass. Catching a pass is control, and two feet, everything else related to advancing the ball is an act common to the game and makes a receiver a runner. In the pre-2015 rules it was the act or the time to do so. I listed some things a runner does a few posts ago, I had 10 things, and I am certain there are more. The thing to ask yourself was after Dez had control and two feet landed, did he do anything that showed the intent to advance the ball? What did he do that can't be explained by momentum to the ground? For me he braced, but you could claim it was to break his fall, but that does not explain moving the ball to his dominate hand, that was nearest the end zone, pushing off is left leg where it went from bent to fully extended to get him closer to the end zone, and extending the ball toward the goal line. Those are acts a runner trying to advance the ball would do, not a receiver trying to possess a pass. That is why it was a catch.