Firstly, it means that they think that our society is a meritocracy (or close to it); this shows that they lack life experience/wisdom. Once you realize how far society is from being a meritocracy, it's literally impossible to feel like an impostor. There are so many successful people who are idiots that even if you were an idiot yourself, you would still be within the norm; I.e. not an impostor.
Another thing about people who have impostor syndrome is that it shows that they feel insecure about their intelligence and/or abilities. Insecurities are typically rooted in past experiences or traumas. Smart people often get positive reinforcement about their intelligence; they don't have traumas or insecurities when it comes to their intelligence.