As for the stereotype about Blacks and Watermelons, I personally think it a lot like the other "Black Stereotypes:"

More often than not, these things that are "Stereotypically Black," are also stereotypicaly SOUTHERN.

Fried Chicken, Grits, Watermelon, and even Chitlins are Southern Delicacies shared by both Blacks and Whites.

I think it really no more than that: Cultural food and tastes that "move" when people of that cultureal region move around the country.

I see lots of people, both Black and White, munch on Fried Chicken and Watermelon...cause they are GOOD!