Chances are - it's a screenshot of a development prototype of the app. It may have had the working name of "4D" and been changed to 6D for release.
Either way, it requires a WiFi connection (which only the 6D has as a built-in feature) - so I think that's the situation.
I kind of share your idea. I think that they were preparing 4D - 40 MP ;-)
Than suddenly came to the knowledge that NIKON gets a new low cost FF. Probably from someone that was testing in the wild. So they decided to make a smaller version. Cut it off and the 6D came out.
I am sure they always have a few CMOS on the table ;-) Just don't know which one when to use. Usually the marketting dep. makes such decisions.
So for the 4D they were maybe preparing some advertisments when a last-minute decision was taken to release 6D. That is why we have a delay from 2-3 months from the NIKON model. They needed that time to adopt the manufacturing details... and tests....
This is my idea ;-)