Answer:
It means his IQ score is better than 91% of the other students scores and scored less than only 9% of the other students.
Explanation:
Percentile is not the same as percentage. While percentage is the score gotten out of 100, whereas, percentile means that you are scored better than that percentage of people.
Thus, for his IQ score to be in 91st percentile, it means he scored above 91% of the other students, and only scored lesser than 9% of the students.