My boyfriend has chronic bronchitis and his parents are both smokers. Is there a connection?

My boyfriend was diagnosed with chronic bronchitis in summer 2015, after a cough that didn't go away for 2 months. He doesn't smoke but both his parents do. They do it several times a day and in the living room (I know, I was shocked as well). My boyfriend lived at home for 19 years until he went to uni - so 19 years of intense passive smoking. The disease had apparently been hiding for a while and it was revealed after he'd been living on his own for a while. He now has to use an inhaler with prescription medicine 2 times a day. on top of other things. Is it just me or could his passive smoking and chronic bronchitis be connected? It just tears me up to think that his parents, lovely people otherwise, have been the cause for their son's shitty health in his early 20s and possibly for the rest of his life :(