These pics show that it's not a joke after all!
We've been fairly dismissive about 4K video on a smartphone. After all, they have tiny lenses, microscopic sensors, and even if mathmatically they have the right number of pixels, the chances of them giving a meaningful enough signal to result in eight million separate patches of moving colour have to seem pretty remote.
Eating our words
But having seen this, we're prepared to eat at least some of our words. Not the ones that said "Not really 4K", but, perhaps, the ones that said "Terrible", "laughable" and "complete waste of time" (we didn't actually say those but are prepared to admit that we thought them).
But look at these pictures. And then look at the video (make sure you set YouTube to show the 4K version, and be prepared to wait for it to buffer).
The first looks sharp enough for a smartphone. It's a screengrab from a 4K video, but it's only around a tenth of the screen, and that original screen was only a 1920 x 1080 image - I don't have a 4K monitor to take a one-to-one screengrab from.
The second is the full frame,reduced from the YouTube 4K image but screen-grabbed from my HD monitor - so is again not the full 4K resolution.
You need to see the video to judge for yourself.