I agree with you on this. I don't know how the refs could have called that an incompletion initially. It was obvious to almost everybody (refs not included) that it was a catch. Even the announcers were on board with it being an interception (even though they did not mention the elbow). If they had called it an interception, I'm not sure that the ref would not have reversed the call anyway due to his foot not being down. I doubt the ref even recognized the elbow being down in the replays.
We've seen this situation over and over again though, where the ref gets the initial call wrong, and it completely screws over the *should be benefiting* team. As evidence, the Steelers and Phins game this week, and the Broncos-Chargers came a couple years back that Hochuli botched. It happens.