Yes, AT proto is about making data available to the public via replication. There's no privacy at all, but it's useful for some things. Hacker News comments don't have any privacy either.

There's another protocol in the works that should be useful for syncing private data:

https://github.com/bluesky-social/proposals/pull/94

I am genuinely confused. Isn't the point of public social media to be... public? Or do you use BlueSky to talk to your friends, instead of Signal?