It doesn’t sound unreasonable. Areas with a lot of smog and air pollution tend to have a higher rate of asthmatics in the population, so I don’t think it would be impossible to think that breathing noxious fumes within your home could potentially contribute to your developing asthma. Personally, I developed asthma after a brutal case of pneumonia in my late teens.. so I wouldn’t rule that out as a possibility, either. Living around smokers prior to this incident could have been causing you chronic lung irritation, which will also contribute to the likelihood of one developing asthma. The pneumonia may have been the “straw that broke the camel’s back,” so to speak. By “smokers” I assume you mean cigarettes… but overall, I can see how frequently breathing in irritants like that could probably be a contributing factor, if not the cause.