I think a better headline would be something like "Limits of alcohol tolerance." After the 4-5 drink-equivalent drink, the heavy drinkers did well on the cognitive test even though they didn't do any better than the light drinkers at the manual dexterity test. It looks like tolerance does affect certain faculties, up to a point.

They also didn't test the light drinkers at the 7-8 drink dose, so I'm not sure we can draw any conclusions there. The heavy drinkers did badly, but they still might have out-performed light drinkers. (If you gave me seven drinks in half an hour, I don't think I'd be able to read the test.)