Africa is not excluded from this world analysis. The listing of blood type percentages simply lists the continent where each blood type is the most common. In this synopsis, Type A has the highest prevalence in Europe and Central Europe, Type O has the highest prevalence in the Americas, Type B and Type AB have the highest prevalence in Asia.
Type O+ blood is the most common across the continent of Africa, but it does not have the highest prevalence in the world of this blood type. 45% of South Africans have Type O blood, but this is not the highest prevalence (nearly 100% of South Americans have Type O blood). In short, the blood types across the continent of Africa are varied and it does not have the highest prevalence of any one blood type.