Actually Im African American , many of the reasons many AA's have rather unique names is because some of them tend to be a combination of other significant names. There is a boy I know with the name "Diontay". His mother named him after "Diane" her grandmother. "Ontavious" her uncle and "Taylor" her cousin. all of these people played a significant role in his mothers life and so thats why the name is rather unlike anyone elses.
there are so many more like:
Shadequa
Kaylashante
Moniqua
Rontavious
Shameeka
these are examples of names that are combinations of other names if you look at it closely.
Believe me I asked my mom the same question youre asking(she chose a rather simple german name for me) and I didnt understand why certain names were so made up until a friend of mine explained it to me.
Most likely "Mandisa" is a combination of names that were significant to her parents.
However I have no explanation for African Americans who name kids after achohlic beverages and fancy cars
Hope it helps!