I did in fact see it was a different person I was responding to. I tried to make my language target neutral. I settled on "rebuttal," as it felt like it restarted the attribution to responding to my post, not your OP, though I suppose using "double down" probably did the opposite. Regardless, I did recognize it was a different person.
But let's be clear. Bald faced prejudice is not rhetorical exaggeration. It's not rhetorical exaggeration to say "black people are usually criminals." Are some black people criminals? Sure. But to pretend that it is therefore somehow intrinsic to that community isn't innocent point making. It's racism.
And sure, that guy was joking. But let's say someone says something racist, I call out the racism, and then someone makes a racist joke in response. I don't think it's "not understanding humor," to call it out when I've already established the problem is the racism.
Prejudice and tribalism isn't a good thing. Even when it's against people you don't like. Perhaps especially then.