Anonym, you are right that as scientists are making progress in studying genes, it seems that all diseases are genetic. Diseases are caused by mutations in our genes (either one gene, or a few).
That doesn’t mean that all diseases are inherited. Some gene mutations are inherited from our parents. Others are caused by environmental factors that have an effect on our genes after we are born and exposed to the air we breathe, the foods we eat, etc. Genetic mutations can also happen randomly. Some diseases are caused by a person with a specific gene mutation being exposed to environmental factors.