True. And looking at their comment history, this "What about black-on-black crime?!" seems to be a recurring bit over the last few weeks whenever people here talk about police brutality. Still, I think it's worthwhile to name and push back on this tactic when we see it, because it's pretty commonly used when people want to minimize or ignore police violence.
Are you suggesting that the user chose their username in honor of Jefferson Davis, president of the Confederate States? I suppose it's possible, but it's patently absurd to assume that is the only (or even most likely) reason for their name or explanation of their intentions.