@tsarstepan,
I suspect that a very slight intoxication makes people less likely to "overthink" their answers to multiple choice questions, and improves the probability to select the right answer on instinct (or "gut feel").
Even when sober, instructors always tell you to go with your initial "gut" instinct on any question you don't know the answer to. Since alcohol reduces inhibition and increases spontaneous reactions, it probably just enhances the tendency to "go with your gut".