I seem to remember it being that you could see anyone at your college. Which made it defacto public because strangers had access to your profile. (You had no access control with your profile). As long as I had a college email I could see anyone else's profile if they were at the same college. Networks were college based.

People were up in arms when anyone with an email address could get in and see their stuff. They wanted to expand their market. I think that was 2005. So in response they hacked in some not very good privacy features.

Maybe I am misremembering, however.