From all three locations (Gumroad, GitHub, ko-fi) I get a bundle on my iPhone and on my PC, only Gumroad additionally offers to download it as a zip-file, and on GitHub there is also a way to download it in a zip-file, but not if you go and get it over the releases-page.
So, if you really downloaded it first from ko-fi and got a zip-file, is it possible that you used a different browser than this time? Because there are browsers out there that believe to serve us well, changing a filename extension, but they only think to serve us well.
For my understanding, it could not have been otherwise. Or have you overlooked something.
Michelist