[_cs2017_]

It is stated almost implicitly in the article.

1) It's in the title: "The Price of Fame" implies that there are downsides to becoming famous, rather than there are downsides to having traits that might make you famous.

2) While the abstract merely claims "associated with" (which is correlation not causation), the phrase "beyond occupational factors" implies that the authors felt they removed important non-causal factors, hinting at likely causal relationship.

And yes, any causality implications are completely unfounded, and so this paper is of low quality.