He might be right.
Congo/Angola contributed the most slaves in the slave trade. A country that shall not be named produced the second most slaves in the slave trade and the Yoruba were either the hardest hit or second hardest hit group from the country which shall not be named. A lot of Yoruba were taken to Cuba, Brazil and the USA. Most of the positive results on AncestryDNA and 23andme for the Country that shall not be named is from samples submitted by Yoruba people. They had some tremendous empires if people are interested in learning about them.
I always advise people to ease into research on Africa, because there is a lot to it. I suggest starting with Basil Davidson, because he is easy to read and he gives a very good overview of the Continent of Africa and who the people were pre-colonialism, which is when there were African Kingdoms. He then eases you into slavery and then into colonialism before there were any actual modern countries partitioned by the Europeans.
Then this book is a good introduction to the slave trade:
I read those books decades ago and his research was pretty good.