Is there even a working definition of what a "filter" is in Instagram, or mobile photo editors targetting social media users (which is approximately all of the mobile photo editors), beyond "a script that fucks up your photo in some trivial but also undocumented ways"?

I'm yet to see a filter that makes your photo look like taken from a specific camera (old or otherwise). Smearing colors and sticking a frame that imitates camera film border does not count.