In the linked video set, the game boy original one is fake, but the game boy color one seems legit (probably helped a lot by the hdma that allows copying tile data into vram during hblank).
Ugh, my naive brain didn't even consider things being faked. I know the Sega Genesis one works in an emulator (I don't have a physical Sega Genesis anymore so I can't try it on an everdrive or anything), but I haven't actually tried the Atari one in any capacity, so that one could be BS.
Theres an old japanese page that seems to explain how it works: http://web.archive.org/web/20121128095253/www.geocities.jp/s...