They are broken down by college graduates. The article breaks it out into other factors. Fact is., give same experiences and degree, some people are treated differently due to the shade of their skin.
You claim to be a college graduate and yet you seem to have a problem with reading comprehension. The parent is pointing out that there is a difference with regard to cultural background between African Americans who trace their lineage back to the slave trade in America and those who come from the Caribbean or even recent immigrants from various African nations. Africa is a continent, not a country. The same goes for Europe. We Europeans are not a large homogeneous group with the same culture and attitudes.