This is in essence, racial discrimination. Yes.
However, when you’re dealing with the creative arts, the conceptual view according to the director or producer is often the overriding decision. So, the theater group may get away with it.
If the director can say she was trying to present a show that featured and glorified blacks in that setting, she may have a point. In some other production, this may not be the case at all. I would find it even more believable that this man was ousted because of age discrimination. He’s in his early 50’s.
A producer’s conceptual view wouldn’t mean shit if races were reversed in this situation.