I'm not convinced it is legitimate but it depends on the resolution. At 320*256@25fps would need around 2MB/s sustained write to chip ram. The footage looked rather higher resolution than this.
The video says it's 640x180 so the bandwidth is similar to 320x256@25fps. However, he played it on FS-UAE, and I doubt that it's emulating the chip RAM bandwidth limitations too.
I totally agree that HAM8 videos will playback on a reasonably powerful Amiga. Even 25 FPS is possible. But that original video was not on an unexpanded A1200 for sure. There was not even one single artifact that I could see from a HAM8 video. I have no idea why the original author of the post would be interested in lying about it.
The description of his last video says playback is in FS-UAE, so it's emulated hardware. From memory, HAM8 artifacts can be avoided/minimised via intelligent use of dithering. I can't remember what tools generated the highest quality HAM8 images, though. Added to that, it's clear that each anim frame has its own base colour palette; just look at the mouse pointer flashing different colours in the bottom right. That means that the colours of each frame have been optimized for that frame.
It would be nice if we could play the anim itself on our own hardware.
Hans