looks like someone might be playing a prank on you, that page is a 404.
access/area51/ even if that was a real restricted area, I doubt they would make the name that obvious, it would be too inviting for hackers to attempt to break in.
this could be accomplished even simpler by sending a forged http request header to your site with the Referer modified to whatever.
its very simple and can even be done with telnet
