Researchers from the University of Texas Medical Branch at Galveston, University of Kentucky, and University of Maryland found that for people 60 and older who do not have dementia, light alcohol consumption during late life is associated with higher episodic memory — the ability to recall memories of events.[...]
Findings from animal studies suggest that moderate alcohol consumption may contribute to preserved hippocampal volume by promoting generation of new nerve cells in the hippocampus. In addition, exposing the brain to moderate amounts of alcohol may increase the release of brain chemicals involved with cognitive, or information processing, functions.
They can't be sure, however, that better memory doesn't cause one to drink more. Not to mention, causation may lie with unmeasured variables that give rise to the link that was found.