Medicine became the domain of the Catholic Church and others. As a result, the former hippocratic teaching that diseases were a natural process in the body and not the result of divine punishment or possession by evil spirits was in many cases dismissed.
This is wrong; or at least, it gives the wrong impression.
During the middle ages, educated clergy accepted that diseases could result from imbalances in the four humors, bad air (miasma), diet, or environment. This was the result of Aristotelian and Galenic medicine: imperfect but the best humanity had advanced at the time. These
naturalistic explanations (not supernatural) were widely taught and disseminated, especially in cathedral schools and early universities, many of which were Church-run.
Author showcases his ignorance in favor of old stereotypes. There's plenty to criticize about the Church without needing to resort to historic lies.