I don't get the feeling this author has much experience with yoga balls, or is just making a statement they want to believe is true and peddling it as fact.
I mean... they had enough of these balls pop while people were sitting on them to decide to ban them. Do you really believe that most of these, which are probably bought on Amazon, etc., are all made of the highest quality materials, and testing using rigorous QA methodology? Chances are, people are buying the cheapest, $10 yoga balls and not trying to find which one will last.
Did they, though? I can't find any news story about catastrophic failures of yoga/exercise balls at the University of Michigan (or another university). The author doesn't link or cite anything supporting this allegation. It may fit someone's "Amazon/yoga ball is cheap/crap" narrative, but I don't buy it when the underlying claim is unverifiable.