Model minority is a term that refers to minority that has a higher achievement than the average population. In the US it usually refers to Asian Americans. It is true that Chinese and Japanese Americans do have a higher income mean than African Americans and Latinos and one that is similar to the average of European-American. However for other Asian-American groups, though this is not true and is a harmful myth that denies that Affirmative Action benefits that should otherwise receive. This term can also refer to Arab and Indian Americans.
What causes a group to be successful or unsuccessful is a complex mix of cultural factors, for example in southern Europe Romanies (in Spain and Bulgaria) tend to be far less successful than the UK Romanies.
Thinking in terms of model minorities encourages racism because it emphasises differences. People come to despise groups that are on average below them while groups that are on average above them are envied.