Riedel knows damn well that there was nothing "controversial" about the production.The diversity of the cast was not controversial and was not debated.
The controversy was about one review by John Simon. What was controversial were Simom's anti-semitic and racist comments in the review. By that point Papp had been casting diversely for nearly 3 decades, so any casting controversy about his productions was long gone.
Why even bring up that 12th Night?
This laziness is all over this article. Reidel finds examples that do not quite fit, and then twists them to fit his agenda. Rather than examining current divisions and issues, actually articulating the differing points of view, he moves to safely burred conflicts from yesteryear without finding any significance they would have for todays situations.