Like, I'm fairly sensitive to anti-white prejudice. Not because white people are some oppressed minority, but because it absolutely gets tiring having to justify your own existence for being born. But this? Man, this is the equivalent of "Americans like hamburgers" or "German humor is no laughing matter". It's okay to embrace a little absurdity, as long as it's not taken seriously by you or by your society.
The historical context is not the same. The watermelon stereotype is an anti-black racist trope from the 1800s that arose from resentment against newly emancipated former slaves. It accused black people of being "happy to do nothing but eat watermelon". In comparison, the stereotype of white girls enjoying pumpkin spice doesn't have the same negative connotation.
Do you actually think the watermelon racist trope is because black people just happened to like watermelon a lot? Because if you do you need to go read up on it, and if you don’t then you need to stop trivializing the history of racist oppression by equating it with a joke about a snack purchase.