I would wager that's a post-manufacturing screen displayed before any firmware has been flashed to the logic board. Notice how quick it was? It was like a bios post, followed by a prompt to initially flash the device.
That might also explain why the image displayed appears to stop above where the screen should extend. If you look at the 5s, the cable in the image on screen extends almost to the home button. But on the "6", it stops well above that, giving the illusion that it has a huge bottom bezel, which we already know is about the same size as the 5s.
It's possible that the initial boot displays in lower resolution, or that they tried to flash a 5s ipsw onto the phone, causing it to display in lower resolution.