My understanding is, but I am not an expert, some groups call themselves as Arabs, possibly for status reasons, and officially they are classified as Arabs. Officially there are black Arabs in Africa. The world media report the fighting in Sudan as being between the Arab militias and native Africans.
In the case of Obama Snr, I do not dispute he is definitely African, but he may be officially classified as an Arab-African.
Barry O Sr. was a Luo who are NOT classified as Afro-Arabs. Even the elite of the Luo never intermarried with outsiders.
Yes, but - is Obama's Kenyan father one of those? No. No, he's not. The "Arab" claims are, from what I can see, based soley on his next stepfather's Indonesian muslim claims in Indonesia. So, does that make Barack an Asian? Nah.