The link has unfortunately been taken down, but the layout of the site and its clear references to a second Mirror’s Edge can be seen in a screenshot posted in the thread. Other posters have also confirmed that the site was legitimate.
It’s unlikely that the site was a mere placeholder, as other unannounced games such as Mass Effect 4 and FIFA 2015 lack support sites. In contrast, announced games such as Dragon Age Inquisition do have Help Centers set up, indicating that a Mirror’s Edge 2 is being worked on. In addition, the fact that EA saw fit to take down the site so quickly after it was found indicates that they didn’t want the site to be discovered.
While by no means an official confirmation, this discovery does raise hopes for a sequel to the 2009 game. The original Mirror’s Edge was largely a niche game, and as such it ultimately failed sales wise. As such, it was generally assumed that a second Mirror’s Edge was off the table, something that has now been called into question.