Yoruba culture

Yoruba is an ethnicity in west Africa. Stephan Palmie asks us whether Samuel Johnson is a yoruba or not? because he was born in Sierra leaone and later became a yoruba. well, i believe that he is still a sierra leonian even though he followed a yoruba culture. Those yorubas were slaves taken from Africa to America. so the question asked is if whether those slaves were yorubas before moving to America. i believe yes, because the culture seems African and they didn't start to follow it when they were taken as slaves. I dont even believe that those people are yorubas because it seems that they were given the name judging the way they looked, for example, that's what happened with Samuel Johnson. So, following the history closely we find out that, questions about ethnicities arouse on whether they should be following that culture or are they following it because they were told to?