Smoking isn't the only cause of lung cancer although a major one. Anything that damages DNA in your lungs will increase risk. Dustin Diamond who also died of lung cancer two weeks before Rush, didn't smoke either. Neither did Andy Kaufman. Only about 10% of lifelong smokers will develop lung cancer over their lifetimes. That's because cancer development is a long complicated process ("oncogenesis") and a number of things have to go wrong over a period of years before cells turn cancerous. Being a smoker just gets the ball rolling.
That makes sense because when I was a kid about half the adult population smoked and yeah a lot of people died of lung cancer but it wasn’t a huge percentage of old people. And a lot of them also had asbestos exposure which I was told when I worked on truck brakes that the combination of asbestos exposure and smoking was very significant in cancer causes.
Nice info, thanks.