considering that, in this situation, he has been described as a "long time smoker", it is perfectly viable. it is conceivable that he has been smoking longer than it has been accpepted that smoking causes lung cancer. and since smoking is also addictive, just quitting because of some ambiguous threat regarding a behavior that has always otherwise done you no harm. it often takes an event to convince one of a need for change. an event like, say, a double lung transplant perhaps?