Science is hard, and that's why science rarely gives black-and-white answers. This study is not the one final word on the matter. But that doesn't mean it's not still useful.

Science is done based on the evidence that is found, and this counts as some evidence. Does it answer every question? Of course not. Does it help improve our understanding of the occurrence of it? Yes.

Correlation is not causation, but where there's smoke, there's often a fire—as these findings continue to be validated (and there have been other studies that find similar links), it becomes more and more relevant to understand why there is such a correlation—to find a causal mechanism, if it exists, or to confirm that it's just spurious correlation.