The problem I have with this study, and other studies like it is that it's presuming intelligence has anything to do with thinking time. It has nothing to do with thinking time. Suppose a very intelligent person with a large vocabulary may take longer and forumulate their answer to a question more carefully.
Alcohol is a depressant and can make you calm and assists your brain in being able to block stimuli, essentially reducing your situational awareness, which would otherwise distract your brain from focusing on a specific task.