You set to create a divide between people to shame one group into acting like the other, which is a classic tactic. The same thing was done with Asian Americans who complained about whitewashed casting in films like Bringing down the house and Ghost in The Shell.
To think that each group should react the same based on their same color, while ignoring social/cultural differences, is setting up a divide and conquer narrative. The Nigerians and Ghanians you met most likely does not have the cultural experience of their identity being represented by huge gollywog style Afros and darkened skin. It completely ignores one group's history by trying to shame them based on the behavior of a "Better Child"