It's not clearly stated. I think what they mean to say is DoS on Facebook using brute force mechanism as testing this would bring down the Facebook system itself. Now manipulating Facebook's server to cause the attack, that'd be different I guess.
> If you can easily cause any website to become an on demand low orbit ion cannon
You can do this with any website that lets users post links which may or may not be automatically loaded (by other users too). There are tons of these around; forums, blogs, etc. See also: Slashdot effect. That's also a true DDoS, coming from many IPs, as compared with a few of Facebook's servers.
