My mistake; the original post doesn't distinguish between the colloquial term "overconfidence" and "overconfidence" as a term of art in psychology. In the early cases, I meant "overconfidence" as a colloquial term meaning "excessive confidence" — that is, a degree of confidence not justified by one's available information. But later, I used the term to refer to the overconfidence effect, which (as far as I know) is only ever measured in the context of multiple judgments.

I'll try to think of the best way to fix the original post, and I'm open to suggestions!

Edit: I think I've fixed it. I've removed the accusation of overconfidence, while still saying that it might be part of the problem. I've also added a footnote explaining that I've edited the original post to correct the error.