Note it was possible to use a Z80 to function as a display controller, people used to do it back in the day...

https://archive.org/details/Cheap_Video_Cookbook_Don_Lancast...

The Galaksija computer used it's Z80 to help generate the video signal. I'm not sure how its implementation compares to your link.

https://en.wikipedia.org/wiki/Galaksija_(computer)

https://media.ccc.de/v/29c3-5178-en-the_ultimate_galaksija_t...