Answer:It is because of his ethnocentrism
Step-by-step explanation:
Ethnocentrism is a term that refers to the fact that someone thinks that their Culture,ethnicity,nationality,religion and race is better than that of other people .
This belief may make someone thinks that people need to convert into his or her religion or they need to start doing things that his or her nation does because the person believes that theirs(culture,nation, religion etc) is the only thing that is the best in the world.
Nathan says the American education is the only best and effective in the world and this probably offended these other students who come from other countries.