LOL. Last names are no true indicator of ethnicity and, even if they were, how many lied? What is 'a lot'?
Are you saying that people did not lie back then on the census and many other things? If your answer is No or Not that much, then we can end this discussion now. If your answer is Yes, then ask yourself, what roles did the Jews play in the slave trade and do your HW, if you need sources/books, I can provide them to you...sources that were written by JEWS themselves and not by the NOI