I feel like this all hinges on the assumption that black people do not proportionally like watermelon and fried chicken more than other groups of people. I'd be interested in some stats on that. A quick search brought up this study which shows that they do https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9884589/
However, now I have to wonder if they eat more chicken than other ethnic groups due to generational poverty and the fact that chicken has been historically the most affordable meat. I didn't have any success finding the answer to that question.
Regardless, those foods are delicious and I'd be happy if a tradition of eating watermelon and fried chicken for Juneteenth became more popular. What really matters is if any significant amount of people actually feel discriminated against for it or if the social justice warriors are picking this fight on behalf of people that don't actually care.