Him saying the slur is not evidence of his racism. The disability does not force him to vocalize things he subconsciously thinks, it forces him to vocalize things he finds abhorrent and wrong. This is also why he's not calling white people "slurs" as some people have mentioned, because he presumably doesn't think those are taboo because anti-white racism isn't real (correct).

Now, the harm that is done to the black people who were on the receiving end is of course still real. But if this discussion starts with "why should being disabled cancel out being racist" it's fundamentally missing the point of one half of the equation (ableism and disability) and it's not going to accomplish anything.

I also find it extremely troubling that the broadcaster who got to farm controversy by inflicting these slurs on millions of black people while scapegoating disabled people and censoring "free Palestine" is now completely getting away with that while the discourse turns into a war between disabled people and black people, which are of course not at all mutually exclusive categories.