I chuckled at that, too. I struggle to imagine what would be on the receiving end of that. I doubt most desktop machines could decode a 60fps 4k MJPEG stream, let alone a phone. Maybe they sell an SOC the other side too.
The encoding side is very expensive with H.264, but as I understand it a lot of work goes into building the right reference frames so that higher compression and faster decode can be achieved.
I wrote a multi stream mjpeg decoder some years ago and it could run three MJPEG streams at 1920x1080@30 on a 2008 Macbook Pro (Core 2 Duo, 2.5ghz ).
And, of course, it's much easier to build a desktop with far more than four CPU cores these days.