Looking at the wiring, I’d be willing to bet that there’s no permanent connection at all and that you would (if you were lucky enough to own such a masterpiece) carry an HDMI cable and power supply separately.
In fact you can see in the video where the kickstand is deployed that there is a right-angled barrel jack connector linking the top and bottom sections (presumably for power): https://youtu.be/sBAsZ0cLV5w?t=19
And in the foreground there is very clearly a black, panel mount HDMI connector.
Then you see the case being opened with a black screen, followed by a finger moving toward the “on” button, and suddenly a cut to a close-up of the on-button that masks the step where additional cable must be connected.
In the shot following the button press there are suddenly more cables connecting the top and bottom half that weren’t there before, and most of the boot process has also been omitted.
It’s all smoke and mirrors and skilful presentation!
Edit: I watch too much Captain Disillusion: https://www.youtube.com/user/CaptainDisillusion
Edit 2: Oh and just to add a dash of real-world experience with this problem: flex cables between the top and bottom half of computers, if not executed perfectly are an extremely common point of failure. Additionally subjecting a regular HDMI cable to frequent bends would eventually cause breakage in the cable. As much as I’d have loved to find a genius integrated solution; Love Hulten made the right choice here from a technical perspective.