It is a paradox. In common usage, a paradox is an apparent absurdity which nevertheless holds up upon deeper investigation. In this case the apparent absurdity

It is a paradox. In common usage, a paradox is an apparent absurdity which nevertheless holds up upon deeper investigation. In this case the apparent absurdity is e.g. "Treatment A is better at treating kidney stones despite performing worse in both trials". Sometimes the word paradox has a slightly different meaning. For example, Russell's paradox in mathematics is the opposite; it takes something apparently well-founded and shows that it is absurd.