I'm not sure what I accidentally stumbled into, but I input my password into this page. After realizing this forum was drastically out-of-date I immediately changed my password just to be safe.

Is this a legitimate relic of the past or some kind of phising attempt?

I *think* it was a preview of the new website design back when they were rolling that out.
It's safe, no worries. That site has been disabled for now though.