How do you know?
This can only be proven on an open source system and I doubt the majority of people uses Graphene on their phones.
Any IPhone or Android user exposes their self-collected biometric data to the wholecworld.
Discussion
I agreed with you up to the last sentence. Just because I don't know with absolute certainty, doesn't mean the opposite is true.
With everything there is a level of trust. We trust that corporations aren't lying always, we trust that white hackers aren't just actors, we trust a lot. Otherwise there are so many unknowns around you, that fingerprint reader is no where near the top of your list and that tin foil on your head is actually an antenna.
