The first 2 paragraphs (the only evidence is the moon's wobble, which must be caused by a large mass inside the moon which shifts position) was news 2-3 months ago. At that time, they said it was an internal ocean, but they didn't know whether it extended over part, or all, of the moon.
Now they measured density changes (= altitude changes while passing overhead), and found that the underground ocean is global. (Density gradient is an old concept. While 2 astronauts walked on the Moon, the 3rd Apollo astronaut famously measured Mascons.)