This is absolutely right. It would be cruel and unusual to pick on some particular word when someone is clearly a beginner in English, but when they are otherwise very good and they make an incongruous mistake it grates. I think people feel better about correcting or good-naturedly making fun of errors like this because it's implied that "your English is so good it's funny that you got that one small thing toally wrong". Of course this is often not so well appreciated by the recipient for various reasons.