Should a math question contain a question that the general public would question? Of course not.
Was the question racist? No, it wasn't, as it is history, not a derogatory statement that a lot of blacks in the US were slaves prior to the Civil War.

Here is some food for thought - most people on here don't seem to realize that slavery still exist today. Africa still has a lot of slavery, as does Europe. Asia also has a lot of slavery. Guess what - they are not only black, they are of all races. Perhaps we should focus on the slavery part of the equation, and how to teach kids that slavery is wrong, no matter what color the person's skin happens to be.