The point Hurston is trying to make is through humor, showing the black people as part of the society of the United States.
Explanation:
She is not <em>“the only Negro in the United States whose grandfather on the mother’s side was not an Indian chief”</em>. In fact, the term "Indian chief" refers to the white owners of the slaves. At that time it was very common for these people to abuse women to get them pregnant and thus generate more slaves, so she is not the only one in this situation.
What the author tries to show with this phrase is the diversity of races is abundant in the United States, since their descendants come in part from white men, for which the author criticizes the racism of people who still do not accept it.
