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

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.

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.

Many reasons: Infections (hepatitis b or c), fatty liver disease (fat infiltration in the liever), autoimmunity.