How is it that my dad got oral cancer if he never smoked?

Many Causes: You wrongly assume that only smoking causes cancer. There are other causes, too. Follow the below link for more info. Hope all goes well with your father's treatment. http://www.cancer.org/cancer/cancercauses/.

It is possible: Smokers are many times more likely than non-smokers and/or non-consumers of alcohol to develop these cancers.