“Open source” [files] means the source of the pdf. If the source files aren’t available with the download, it’s not open source.
I hope it doesn’t come across as a small point, as it’s a pretty big deal to me. I’ve spent years looking about for others doing open source RPGs, but most people using the word ‘open source’ mean something like ‘copying this pdf is okay’, which makes it very difficult to find open source RPGs under all the false signals.
The licence doesn’t appear on the page.
Itch lets you select a licence, which will help people search. Under the game, Edit --> Metadata, and select which creative commons licence (there are many).