The causal claim is itself a (stronger form of) correlation, so how is that a contradiction? They claim:

1. To demonstrate a causal pathway

2. There was not a previous correlative claim that this merely strengthened

Also, given it's in an open access journal, you can trivially verify from the source rather than rely on a press release. "we describe a pathway wherein sleep fragmentation raises inflammatory-related white blood cell counts (neutrophils and monocytes), thereby increasing atherosclerosis severity" [https://journals.plos.org/plosbiology/article?id=10.1371/jou...]