Is it correct to understand it like this: Keychat uses Nostr for handling user identity and message delivery, but uses a different encryption protocol for the actual message encryption? And the reason for doing that is because Nostr alone, even with something like NIP-17, can't fully hide the recipient and doesn't offer complete encryption — so this is meant to address those limitations?

If that's the case, does it mean that i can't have a conversation with a regular Nostr client user at the level of encryption and privacy that Keychat promotes? Would it just fall back to the standard level of encryption provided by typical Nostr clients in that case?