Developer Jack Underwood took the dimensions from the recent FCC approval of the LG D820 that has been pretty much confirmed as the Nexus 5 and compared them to the Nexus 4. The result? Despite a larger screen size with higher resolution, the Nexus 5 is actually smaller in every dimension.
If there were any lingering doubt about the match between the casings shown and the device slipped into the KitKat video, the animated GIF below seems to provide conclusive proof …
Gus Janssen turned the case image to match the orientation of a frame-grab from the video to produce this: