Not trying to defend the decision, but as far as I know, the reasoning is that if you charge significantly less than you could, it might be because you have other undisclosed agreements with the tenants, like them doing some extra chores for you, repairing the flat or something else. This way, you could avoid a lot of taxes. The sentence also doesn’t seem to be a fine in the narrow sense, but rather a demand of additional taxes. If I’m not mistaken, it’s perfectly legal to charge very little for a flat, but you still have to pay taxes as if you would have rented it out for a regular price.

I think the text tries to make the point that it doesn’t work not because but despite him being black. The argument Perry and others make in this case is not one in the form of material benefits but rather moral ones. A member of a marginalized group makes it big, which is supposed to inspire others from this group. The point is that this form of trickle down economics works just as badly as the “regular” one, which is hardly at all.