[lucgommans]

I'm fairly sure you must have gotten a fake f-droid store that installs malware instead. I didn't know those were out there.

The real one can be found at: https://f-droid.org

You can also download individual apps (APK files) from the website, so you don't need the store if you don't want updates. Also note how Spotify is not listed if you use their search, because (like others already said) it's not open source and thus not on F-Droid.