Some of them may have been lying rather than seem like the odd one out.
When I was a kid, we were not allowed to talk about doing well in school. It was against school rules (grounds for punishment) and also discouraged by parents (showing off).
When I went to grad school and encountered other cultures, people tried like anything to get me to tell them my grades. I would say, "I was satisfied with my score." They assumed that meant I was a poor student. Nope, I was one of the top students, I just wasn't brought up to share that with people.
Another thing - I have a friend whose son is a good student, but he is having a hard time in high school math because of the way it's being taught. Basically it is NOT being taught, the kids are supposed to learn it themselves in small group committees. This boy is trying hard and getting Cs. Very frustrated. It is likely he has classmates doing even more poorly, not because they are idiots or jerks, but because they are not getting the support a minor student ought to get.