He was obviously down in replay but everyone, including the refs thought they saw a TD, so the TD was called. A vast majority of the time, if there is any doubt on the TD, they call the TD and let the film sort it out. But in this case, it was in the last seconds of the game which invoked the 10 second runoff. But if it had been a TD, and not called a TD, then there is nothing to review on the play, and lets say the Lions don't get in. Then they would be pissed that the original TD had not been called.
Could the Lions have gotten to the line, and gotten another play off? Maybe, but there was no way for them to get a huddle to get a play call out there to their players, and its 4th down so they cant spike it. The odds are against them making another play, and the odds are even greater that they get a procedural penalty because no one has time to line up properly. However it would have been better for the Lions if the correct call had been called the first time so they would have at least that chance. Small though it was. Horrible way to lose a game.
Go Falcons!!!