Dr. Michael Polen, another researchers within the study, made the following comment within the EurekAlert article: "Even after taking these other health-related attitudes and practices into account, there was still a small but independent relationship between moderate drinking and better self-assessed health."
And, "Previous research has linked moderate alcohol drinking with cardiovascular benefits, so that might be the underlying reason moderate drinkers report better health. It's also possible that there are additional factors we didn't measure that account for this positive relationship."
The researchers involved in the study and the paper are: Carla A. Green, Michael R. Polen, Shannon L. Janoff, and Nancy A. Perrin (all from the Kaiser Permanente Center for Health Research); Michael C. Leo (from the Oregon Health and Science University); Bradley M. Anderson (from Addiction Medicine, Kaiser Permanente Northwest); and Constance M. Weisner (from the University of California and Kaiser Permanente Division of Research)