As I understand it, the original study suggested a bias, which causes us to assume that our abilities are closer to the mean distribution than they actually are. The example about the language test misses out on this entirely.

(Regarding that example, a person may even withstand the confrontation with the test score, like, "I guess, even a native speaker doesn't get more than 65% on average", or, "99% is surely not that unusual, everybody with a decent understanding should get a score like this".)