How can a person have cirrhosis of the liver if he is not a drinker or drug user?

Most aren't! There are a number of causes of cirrhosis including: too much fat in the liver (a.K.A. Nash), viruses that were not necessarily contracted by using drugs (hepatitis b/c, others), metabolic diseases (hemochromatosis, wilson's disease, alpha-1-antitrypsin deficiency, etc), autoimmune processes (autoimmune hepatitis, pbc, psc) and medications.
Cirrhosis. Cirrhosis is end result of scarring. It can happen due to other disease processes that can cause scarring including autoimmune hepatitis, hemochromatosis, nash and others.