I doubt it's "hacked", though it is down. The dreaded "error establishing a database connection" screen is just a generic WordPress error that can show up for a variety of reasons, usually because the database services of the host are down, but the PHP hosting is not (this happens more than you might think, even without malice, depending on the host). It could be a DDOS, but I doubt it's been hacked. A hacker would normally replace the site with something else (if possible), rather than just disable it.

Then again, it could be hacked, and the hacker is covering his trail. This I doubt.