Anyone could get to them; they were live links that looked just like that picture. The links looked like this:
https://www.ninjette.org/forums/blog.php?cp=18
It was a link straight to a custom block. You can go to that link now, and it should show a no permissions message, as I banned those accounts and changed the perms so nobody could view any part of their blogs. But I then started to go through all similar links by changing that last number, and found a handful more that had crept in, some as old as a few months back. What is weird is that once someone finds a hole like that, typically they would flood it with hundreds or thousands of like pages; this time it was under 30 so it was easy to clean up.
But to your point, I'm not sure what use they got out of those links if there was no easy way to link to them from elsewhere on this site. Somehow they must have been posting them elsewhere on the net, as the automated brand-protection bots that alerted me apparently found them.