[greysonp]

They don't explicitly state it in the article that I can see, but the PICO-8 is 128x128, and it appears that their output images were constrained to that. Your dithered images appear to be much higher resolution. I'd be curious what dithering would look like at 128x128!

[mezentius]

Dithering is used quite frequently in PICO-8 projects at the “native” (128x128) resolution. Here’s an example from a few years ago: https://www.lexaloffle.com/bbs/?pid=110273#p