If you post in public, it can be scraped; that’s true on Bluesky as well as the Fediverse and also on the centralized corporate platforms. It’s something you have to be mindful of when posting. Using privacy-conscious walled chat apps is the better option for people who want to avoid that, but even those can have leakers in the group chat.
BTW, the Fediverse equivalent is called Friendica and it also supports more platform protocols than just ActivityPub.