You can do better than average but still overestimate yourself. And in a world where people judge by appearances, that can be a real advantage.
The 'relative overplacement' in the first table (the extent that participants over-estimated their own performance) is a correlation of 0.04, while the 'actual rank' is a correlation of 0.13, both in comparison to 'subjective social class'. There are a lot of correlations of higher magnitude than 0.04, so it's disappointing that the article attempts to focus on nothing else.