Note that the scientists themselves do not claim a causal effect, but only association.
They claim causation in several places, albeit sprinkled with perhapses and maybes. From the abstract:
potential windows of alcohol intake that may confer a net beneficial effect
From the Comment section:
...the benefit of light to moderate drinking remained in a range of undoubted public health value (15%-18%)...
...the maximum protection conferred by light to moderate drinking...
...the “real” (maximum) protection against total mortality associated with low levels of alcohol consumption would still be higher than 10%.
This is all causal language.
My roommate recently sent me a review article that LW might find interesting:
Personal observation says that LWers tend not to drink very much or often. Perhaps that should change, to the degree suggested by the article?
Full article here.