Why people are getting confused is because a stretch for the endzone is a football move and a football move means that if it pops out after it hits the ground then it would be a fumble if not touched. Listening to Dean Blandino on NFL Network he says that they felt that the stretch for the goal line wasn't obvious enough that's why they ruled it incomplete and why they felt it was in the process of a catch. Being a Cowboys fan I can see that being called either way with the explanation he gave, it looks like Dez is trying to score, but it also isn't as obvious as other lunges for the goal line, I think the fact that he was going down before he stretched for the endzone is what made the choice easier for them to make.