Normally when looking at an app on F-Droid you'll see the multiple repos available to download it from all on the app's page. Whether it's Izzy, F-Droid, etc. Why does Organic Maps have two seperate app pages on F-Droid? One only lists the F-Droid repo download and the other just for Izzy.
Because they have different appid. Izzy version is app.organicmaps.web fdroid version is app.organicmaps (you can see this in the url). Google version uses the same appid as fdroid. You can't have two apps installed with the same appid, but this way you can have both installed at the same time.
I guess organic devs wanted separate appid for their 2 versions and fdroid just went with the default, original one.
So the 3 versions:
Web: built by organic devs, you can download this from github releases, scraped from there by izzy
Google: built by organic devs, you can download from github or from play store
Fdroid: built by fdroid build server, signed with fdroid devs' key.