He was not clearly short. The one and only replay they showed seemed to confirm the football crossed the line to gain before he was out of bounds despite what the announcers said. It doesn't matter where the ball is when the ball first crosses out of bounds. Instead, it matters where the ball is when Hartman is officially out of bounds, and he was not officially out of bounds until his right foot touches out of bounds well beyond the line to gain. Once his right foot touches, look at where the ball is. It certainly looks like it is well past the line to gain. For some reason, the announcers focused on where Cody Simon hit Hartman as he was going out of bounds but didn't focus on where the ball was once he touched out of bounds. Regardless, there was no indisputable video evidence showing he was short. If anything, the evidence actually confirmed the original spot.
Not that any of this matters. This one play isn't the reason we lost but I don't think we should let the refs off the hook for making a bullshit reversal.
Here's a video showing the play and replay.