Even if you are logged out.
I am not an facebook employee so if i just paste the url in address bar and enter it, it shows: is_fb_employee: false with my UID.
If i logged out, it shows UID: 0 with is_fb_employee: false.
It's a nice idea to attract ppl from different site and based on the site domain, give them relevant career page url. (May be an intern project)
So for HN, it's engineering career page, if the referral site is relevant to some other domain (i.e. sales/marketing) then they will give http://www.facebook.com/careers/department.php?dept=sales.
Not sure how much data facebook have of other websites for categorizing majority of the websites in to different domain, but i feel Google can do much better with the same concept.