It's even not terribly hard to take control of a domain name even without social engineering. Typically, most registrars just require a copy of your DL on company headed notepaper and some trivial other stuff. I've had to do it for domains that were legitimately our company's several times.
Though with that said, security really shouldn't depend on DNS if it's being done properly. I'd be interested to hear what the actual method of attack was just to see if it's one I've heard of.
This was explained in the blog post but essentially they redirected emails to a server under their control and got sent a password reset link.