Cookies probably? The site probably knows your IP address hints showing you that info while logged out.
I'm at work, no cookies or anything are active here. And I don't think I visited the site with this pc at all until I tried the link.
But it seems they fixed it.
As I said, I got the message before I logged in and after I logged in. Now it shows a complete different page after logging in, saying that I dont have access to the page. When logged out it prompts me to log in.
edit: Now after posting this the page tells me that I was selected again, logged in. Seems there is something wrong with the page.
Or I got selected in this second