Actually, I'd guess this is another chapter of the old story at http://www.koreaherald.com/view.php?ud=20180523000780 The source material would be the mineral monazite, which contains
high levels of thorium rather than radium. Indeed, monazite is known as a thorium ore. And since Th-232 eventually decays to Rn-220, we'd pretty much be talking about thoron here. Since thoron is of course an isotope of radon, I think the study just didn't differentiate between isotopes (i.e., "The ... data ... lacks thoron content."), and the "radon" referred to in the article is thoron, not Rn-222.

Hi Kevin. Why would there be a high monazite content in a pillow?

Brian. The monazite in the bed was inserted to produce negative ions which Koreans generally believe to be a health benefit. The mattress company thought they could sell more mattresses if they claimed it also produced negative ions. A purchaser using a radon eye placed it on the mattress and got a high reading thinking it was radon. Actually it was thoron because the radon sensor is on the bottom of the radon eye and is sensitive to thoron. The government initial said the mattresses were safe because they measured low radon levels. Later they retested it for thoron and it was 9 times above guideline exposure.

Because thoron is short lived, 55 seconds, it actually is not a great idea to sleep on a thoron source. All the mattress were re-called.

Thanks, Bill.