It's in response to this news article about worrying about worrying about (the doubling is intentional) the stereotype of "black people and watermelon".
I think I led a sheltered and somewhat oblivious existence, racism-wise, while I was growing up, despite living in the South from the mid 70s to the early 80s, and attending (and being "bussed to", in fact) an elementary school that had been integrated only a few years earlier.
My (white) family ate watermelon constantly. So did everone else, both white and black. Watermelon is cheap, it grows well even in bad soil and inconsistant rain, it's easy to plant and even easier to harvest, it was sweet but not cloying, it's easy to chill and keep cold, even with the technology of a century and a half ago (just put in in the creek for a few hours), and it was "cool and refreshing" on a blisteringly hot summer day.
It was always part of the fun of going to visit family down in Mississippi, in that there were so many different kinds of watermelon to chose from, and to pick right off the vine. (Mmmm... yellow watermelon...)
I was never really aware of the "blacks and watermelon" stereotype until I encountered "sensitive" people complaining about it online.
Watermelon never meant "black food" to me. Whenever I would see the stereotype on old cartoons, I didn't think "black", I thought "south". If it was stereotypical of anything, what it symbolized was "summer in the south".
Now, I will admit to occasionally using the term "watermelon" as an insult. It refers to someone who claims to be "just" an environmentalist, but when you look at their actual motivating philosophy, they are in truth a totalizing "hard" leftist. Green on the outside, but red on the inside...