It's still a problem they should fix (clearly they're not making it obvious enough that you're making your chat public), but that hardly fits Mozilla's accusation of "quietly turning private AI chats into public content." Disclaimer that I have not seen the UI, maybe it's much more misleading than it sounds.
To be fair, Meta has a history of pushing people towards sharing when they wouldn’t otherwise do so. Doesn’t explain the petition’s wording, which suggests interactions are public by default.
You have to explicitly hit a share and post button in order to post to your feed.