"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.
I don't know if Google docs count as a 'source file'. It's clearly the source. Is it a file? I guess everything's a file if you go by the UNIX definition, so 'close enough'?
Licensing riddles aside, it looks great, and it's nice seeing a fast-paced intro that gets straight into what the game's about.