This is not the full code: "A small part is not published because it implements tests or security critical blocks".

Even this published code is half proprietary and half free software. The Android and iOS apps are under a custom and restricting license. The protocol implementations and the Bluetooth SDK are made by INRIA and placed under Mozilla license. The server code, written by the CapGemini corporation, is proprietary and published as a big tar.gz.

On a side note, the Italian alternative solution has a much better documentation of the process, and a Affero License on the whole code: https://github.com/immuni-app/immuni-documentation

Immuni clearly states that it leverages the Apple and Google Exposure Notification framework. StopCovid19 does not state anything like this, so it's unclear what its restrictions are. IIRC, iOS a limitations on bluetooth control.

This didn't got enough attention, there are still companies marketing their own binary obfuscated ones.