No they actually didn’t. News reports have used the ‘new organ’ language. The actual paper is here:
And the scientists who wrote the paper are hesitant to call it a new ‘organ.’
“It is fair to say that histologists [and] pathologists have long known that there is an interstitial space and that it contains fluid,” Anirban Maitra, a pathologist at the University of Texas MD Anderson Cancer Center who did not participate in the work, writes in an email to The Scientist . “The claim that it is a hitherto undiscovered organ, and the largest one ever at that, seems a stretch,” he cautions.