bronchiolitis obliterans is popcorn lung, and there are far more than one known cause.
Bronchiolitis obliterans has many possible causes, including collagen vascular disease, transplant rejection in organ transplant patients, viral infection (respiratory syncytial virus, adenovirus, HIV, cytomegalovirus), Stevens-Johnson syndrome, Pneumocystis pneumonia, drug reaction, aspiration and complications of prematurity (bronchopulmonary dysplasia), and exposure to toxic fumes, including diacetyl, sulfur dioxide, nitrogen dioxide, ammonia, chlorine, thionyl chloride, methyl isocyanate, hydrogen fluoride, hydrogen bromide, hydrogen chloride, hydrogen sulfide, phosgene, polyamide-amine dyes, mustard gas and ozone[citation needed]. It can also be present in patients with rheumatoid arthritis.[9] Certain orally administrated emergency medications, such as activated charcoal, have been known to cause it when aspirated.[10] The ingestion of large doses of papaverine in the vegetable Sauropus androgynus has caused it.[11] Additionally, the disorder may be idiopathic (without known cause)
https://en.wikipedia.org/wiki/Bronchiolitis_obliterans
Anyways, they're both disease of the airways that are the result of inhaling harmful things. Even though the wiki article doesn't state smoking specifically, I'm not convinced it couldn't be a possible cause. I don't really know enough to argue any further than that, and I don't think it really matters for this thread. They're both a type of bronchitis, but I was wrong to say they are the same. I thought popcorn lung was a slang term for copd.