The movie was filmed without permission, what makes you think it couldn't have been shown without permission?
Good Chinese folk can find ways around unjust restrictions just like any other country in the world. The first "festival"was held in a library in the University, probably not the type of festival you are imagining.
They operated for less than a month, could have gone unnoticed?
And no I don't think it's weird phrasing. It's absolutely common practice to get permits to film in public places and historic sites: https://www.thefilmfund.co/how-to-get-film-permits-and-location-releases/
If you're filming on private property your supposed to get they owners permission too.
If a Australian film did some guerilla filming I'm sure that would be mentioned in it's wiki because it can serve to promote the movie.
Edit: try googling "movies made without permission" https://www.dailyhindnews.com/top-10-movie-scenes-shot-without-permission-its-all-illegal/