OK, I think I understand. What the data from the original experiment actually shows is that people at all skill levels are pretty bad at estimating their skill

OK, I think I understand. What the data from the original experiment actually shows is that people at all skill levels are pretty bad at estimating their skill level- it's just that if you scored well, the errors are likely to be underestimates, and if you scored badly, the errors are likely to be overestimates, by pure chance alone. So it's not that low scoring individuals are particularly overconfident so much as everyone is imperfect at guessing how well they did. Great observation.