Hmmm... I would hazard to guess that 'most people' with a Europe centered educational background understand that there are nationalities/ethnicities such as Irish(American), German(American), Italian(American), Spanish(American), etc. Likewise, 'most people' are aware of there being such places as Japan, China and Korea and 'most people' are aware that there are at least generic ethnic groups in America from each. Whether they can distinguish between various ethnic groups is irrelevant. The issue here is with what was stated from the beginning:

"...while terms like Nigerian-American (or terms like Japenese-American, etc.) exist, people take swipes at African-Americans (aka Black Americans) because there are Whites, e.g., from African countries."

So the distinction issue was never about whether 'most people' are familiar with or happen to "care enough" about Africa or her various ethnic/nationality groups. The issue is with those who feel the need to disparage the nomenclature-term AFRICAN AMERICAN in complete disregard to its distinct character and the obvious distinction between the national/ethnic nomenclature of people with an unbroken connection to their national/ancestral/ethnic/cultural homeland or center and those, Blacks/African-Americans who, by historical circumstance, don't have that same unbroken connection.

The fact that certain people choose to disparage the AFRICAN AMERICAN nomenclature betrays the idea that they "don't care enough." For some reason, they feel compelled to speak pejoratively about the nomenclature-term; often without provocation.

Perhaps, I could understand the reactions I've seen better if the actual term had particular cultural/ethnic relevance to them - i.e. if they were 'Black'. At least then any rejection or objection to the term would be part of their expression of what does or doesn't define and, therefore, pertain to them personally.