There are plenty of North Africans that are dark-skinned, so they won't automatically assume the person is BSing. Secondly, it seems wrong to tell someone who's family is originally from Africa but migrated to America, that he/she is not African-American. And many people in North African countries are not full Arab, even though they speak Arabic. Who is to say that one person has some African in him/her vs. the other. What about South Africans? Regardless, adcoms are going to judge you if you put African-American and you're from North Africa, so it's probably wise not to do so.