A seller, ignorant of it's unenforceability, afraid of getting sued.
As one of the greast jurists in American history, Judge Wapner, used to say, "What are her damages?"
He told them about the covenant out front and didn't attempt to hide it.
By the look of his house he doesn't have the money to take chances with a lawsuit over the sale of his house.
By his age and the look of his house he needs the money and just wants a quick sale.
He may be under the impression that by agreeing to the covenant when he purchased the house he is liable for the conditions of sale and he can't afford legal advice to determine if he is liable or not.
The Pitts house is many times more expensive, lavish even, compared to Rufus' humble digs.
This looks like a case of a comportable middle class Afro American professional couple taking advantage of a not too bright but decent poor white guy to get some publicity and a cheap revenue property.
Lord I never thought I'ld live to see the day when I would say something like that.