I don't care what Izzy does. Other repos like the Guardian Project, MicroG, Bromite, NewPipe, Calyx use correct verbiage. But the only thing that matters is F-droid and what they say, so let's look at that link you provided:

Known Repositories A list that tries to keep track of known F-Droid compatible repositories.

Notice it says F-droid comptiable repositories, not f-droid repositories.

And then following that link:

These repositories are compatible with an F-Droid client application. The F-Droid project is not responsible for any third party repositories.

Again, F-Droid doesn't want 3rd party repos to be confused with itself... so yeah, I take issue with calling 3rd party repos F-droid repos. It's just dumb to do anyway for anyone with experience with package managers. If I add some 3rd party repo to Ubuntu, I'm not going to call it an Ubuntu repo.