That's the real reason. "Minorities do worse because of racial discrimination" doesn't really fly when Asians do better than whites on numerous metrics.
As do immigrant Nigerians, who are presumably included. All minorities aren't subject to the same levels of discrimination. This should be obvious given the historical context which drives much of the discrimination. I don't think it is a coincidence that the model minority stereotype was created at the height of the Civil Rights movement.
Sure it can as long as it makes success harder but not impossible. You are looking at a self selecting population which need not look like the norms of either the US or Nigeria.
Really, immigrants and the direct children of immigrants tend to do well in the US as long as they are not part of a mass migration.
Asians are a huge group of people. The academic and economic success of people from south-east Asia is vastly different from those that come from northern Asia.
That's a poor excuse not to break out and list their extraordinary success. Asians lead in median personal income, median personal wealth, household income, household wealth, life expectancy, employment, lowest crime, education attainment, etc.
Hispanics are a huge and diverse group of people too. Yet they almost universally get lumped in together.