How did the Scottish and English surname and placename Coker end up as a common surname in Nigeria as well?

If I may have a guess, I will look for the obvious reason: Nigeria was a British colony.

True, but not only is it the only British name I've ever come across as a Nigerian one (also across the west coastal countries like Sierra Leone) it is not just a handful of people but almost the equivalent of Brown or Patel there. If it was one British family behind it they must have employed a vast number of people to spread the name so far and wide.

I have however just discovered an escaped slave, Daniel Coker who left Maryland for Sierra Leone in 1820. Now if he alone created thousands of family across West Africa that is pretty impressive.
https://en.wikipedia.org/wiki/Daniel_Coker