@thibaultmol you can get this information via our F-Droid client.

Go to Settings -> Manage installed apps. There you find all apps that are available via your configured repositories.

To check if it was installed via another source, you have to click on each app (or the ones you're not sure about) and scroll down. When there are versions available, it comes from F-Droid. When there's a text about "no compatible signature" it's most likely from another place.