That's just propaganda. You never been down there so you wouldn't know if it's true or not. I also heard the notion that all UFO's have came from the water from multiple members of the U.S. military branches.
How is it propaganda? Its simple physics. The article never mentioned there being ACTUAL oceans beneath the surface. At least that wasnt my takeaway form it. If you look at the size of the transition zone you can imagine there being large amounts of water there without it being in liquid form. The pressure and temp just doesnt allow for liquid water to exist. The bolded is just not a very good analyses of the article at all. No one will ever know because no one will ever be able to drill down there. We use logic, trends and empirical evidence as bases for hypotheses.
EDIT: for those who care, an article about another huge reservoir from 2007, using seismic evidence.
http://news.nationalgeographic.com/news/2007/02/070227-ocean-asia.html
As you can see, the water is just a small percentage of the rocks. The vast area of the regions is what makes it add up to "ocean" sized amounts of water....which is actually part of the rocks chemical makeup at this point.