It's likely more of a Japanese problem. She can't get first place because she did everything by the book. And therefore, her answers are the teachers' answers. Alves likely questioned the inaccuracy of the teachers' answers and provides a more thorough or correct answer that not even the teachers can get right. Therefore, the teachers have no choice but to accept that they're no match for his knowledge.
Or maybe it's just that there were questions that the teachers got wrong, but he corrected it. Technically, Nanari didn't answer wrong, because it's in the textbook. How could Nanari know that the textbook got it wrong? Therefore, the teachers can't mark her answers as wrong, but because Alves pointed out what was wrong, he got bonus marks.