I don't believe this. Africans in West Africa, South Africa, Central Africans and East Africa (excluding the Horner peoples like Somalis) are all Bantu type black African people. Genetic tests between Nigerians and Ghanaians indicate there is little diversity between them, so they are basically the same and related people. The same relatedness exists in Central and parts of East Africa (in, for example, the Luo of Kenya) too. The base relatedness is enough to bring Africans together inasmuch as they have a common enemy and seek commonalities within themselves for which to bond. My support for this theory is that this already happened in the Carribean and in other parts of the world where far-reaching black African tribes bred and live together.
What genetic testing are you writing about? If the people of Ghana and Nigeria were similar then how would geneticist be able to distinguish genetic markers between people in the two countries?
Ghanians and for that matter people from the Ivory Coast are mostly Akan and Mande people. The Akan people (Asante, Brong, Baoule, Fante, etc.) migrated to modern day Ghana from the kingdom of Ghana. The Mande people (Bamabara, Dyula, Mandingo, Soninke, Wolof) were the creators of the Kingdom of Ghana, Mali and Songhay.
Nigerians are a lot of different groups and they are not that closely related. The Yoruba people have historically been pretty sedentary in their lands in modern SW Nigeria and Benin. The Fulani people are not even from Nigeria; they migrated there, but no one knows for sure where they are originally from. The Hausa people have ties to the Chadic people to their east, while the Igbo are considered semi-Bantu.