Apple is very much in favour of user privacy, as long as that privacy means "protecting your data from third parties". When it comes to the data Apple itself collects, they're far less conservative. They don't share information derived from their massive databases per se, but they do keep track.
Thanks to Apple and Find My, stalking people is easier than ever. The company can look up where you are and where you've been. They'd probably fight a court order to provide live location data to ICE, but who knows what that'll mean with the current American government.
Even on iOS, user data ends up in the hands of data brokers through ads. They're not supposed to collect all that data, but that's not stopping an unethical company from trying.
Android's privacy issues are there, but only if you're protecting your privacy against companies. If you're trying to protect your privacy against the government, there's no difference, really.
I think this is what the Graphene posts are trying to say.
As others mention, having a web app would make a lot of sense.
While I don't want to assume regular fed honeypot, we can at the very least be certain that it's an app made by an Apple Kool-Aid drinking person. iOS is, in many ways, more susceptible to governement subpoenas than an Android app would ever be. Sideloading, UnifiedPush, maintaining a connection to a server to handle notifications yourself are all more secure than just trusting that Apple will not just hand you over to the cops.
In addition, if the author is worried about a subpoena, it means that they're US based. Which is an absurdly stupid thing to do if you're going to make a fascist-reporting app while living in a fascist country.