> Wait. They think they didn't do well, got an offer, but turned it down because they think they didn't do well on the interview?

Yup. Happened to me: I felt like I did poorly in one of the interviews and had to ask myself whether I'd be happy in the job if the day-to-day was like the interview.

It probably wouldn't have been, but I had another offer on the table and the negative experience swayed me in the direction of the other offer.