I believe he said it would be a woman, not a black specifically. But that is merely semantics, and I don’t know enough to argue it.
I know only a little about Harris, but I’m happy to see a female running mate that can string together some coherent thoughts. Last time one of the two major parties had a female VP candidate, it sunk that ticket’s chance of being elected. It’s a bonus that they picked a fairly moderate-left in Harris, it could have been much worse.