I've actually just been collecting doujin for the first time in my life in the past few months (for Psychic Force, a relatively obscure fighting game from the '90s of all things, but such great fun... Of course I had to run to the linked webshop and search but didn't find anything really up my alley). I had already noticed that use of the word "genre." Once upon a time there was a site called "Burned for Fandom" that was sort of an isolated early attempt at fandom advocacy and IIRC started with someone getting sued by Anne McCaffrey for selling Dragonrider fan-art, and I recall that person referring to it as working in McCaffrey's "genre;" actually a trace of the site is still online and still uses the term that way.