Bluesky says and looks like it is demanding it because of user account settings. Public user profiles are publicly viewable.

https://news.ycombinator.com/item?id=46389747

He set his posts to be viewable by bsky users so long as they are logged in, knowing that anybody can sign up and do so. (I have chosen not to sign up; thus my original question.)

The obvious reason one might do this is to allow blocking specific problematic accounts. It doesn't demonstrate an intent to keep this post from reaching the general public.

So I still think your rush to flag was unwarranted.