People with a high IQ know it's smart to play dumb in these specific situations1. The problem is they don’t know anything about that person, so they don’t know how they should act to be memorable to them in a good way. That’s when someone who’s really smart might have to dumb themselves down a bit. But if whatever is being discussed is totally outside their area of expertise or looking really smart is irrelevant, they won’t make a big deal out of it. That’s another time when someone who’s really smart might not want to let their intelligence show.