Maybe unintentional ways to leak data,
Yeah, that’s what I think it may be. Just like Apple reporting on all apps you open on un-encrypted HTTP calls and a few other things.
Not only that, https://sneak.berlin/20201112/your-computer-isnt-yours/
Signal’s defaults are pretty good about that. Push notifications are both opt-in and the information they send can be selected by the user. You can have it say “new message” and that’s it. Or the senders name. Or the whole message.
I agree that it’s not intuitive that that’s a leak to most people, but push notifications are kind of wonky how they work.