The story
Perhaps patterned after the Portuguese casamento de rapôsa, literally "vixen's wedding", used in the same sense. The Portuguese phrase may have been changed to casamento de macaco, "monkey's wedding", in Portugal's southern African colonies. Alternatively, it may have entered South African English from the Zulu phrase umshado we zinkawu, which literally means "wedding for monkeys".
Etymology from Wiktionary, CC BY-SA 4.0.