The title of the article on arstechnica comes from the following quote, a few paragraphs in
Though few patients appeal coverage denials generally, when UnitedHealth members appeal denials based on nH Predict estimates—through internal appeals processes or through the federal Administrative Law Judge proceedings—over 90 percent of the denials are reversed, the lawsuit claims. This makes it obvious that the algorithm is wrongly denying coverage, it argues.
While they are correct that error rate applies to the number of misclassified cases (denied when it should not have been), it’s only 90 percent of the denials which are appealed which are overturned. As stated in the quote above, few patients appeal their coverage denials, so it is possible the error rate is much lower as presumably the denials which are not appealed would not be overturned at the same rate.