No idea, but as those are closed source one can have the same doubts, so you need an OpenSource alternative to the API, which is in the works in order to be used in that app: https://github.com/theScrabi/CoraLibre-android-sdk/ and https://github.com/corona-warn-app/cwa-app-android/issues/75

That combined with an Android based on AOSP and trust issues should be reduced (while the bad government can still track you using cell towers and for that app one could still place Bluetooth beacons everywhere and the server's could still store more information (while the only keys transmitted are those of infected, which is quite little) ... so yeah, pick your level of conspiracy