Since you have no symptoms it is entirely possible that the diagnoses is wrong. However, if you want to be sure, then visit a pulmonologist to get tested. There is, however, a simple test you can do yourself. Get a peak flow meter. These are inexpensive and can be found on the internet, but I don't know if you can get one in Korea. I uses one made by "Assess." You blow into it and it tells you how you score compared to norms of men your age and height. Because I have emphysema I have one of these meters. Most people with lung problems use them.
In other words, they are saying you have mild COPD. When my father when for a CT scan (he had stomach cancer) the results mentioned dmild COPD, it was a surprise.
I believe the only way the X-Ray would show it is if your lungs are hyper inflated with barreling of the chest. Only a CT scan can be sure.
An ordinary chest x-ray would not be sufficiently reliable for a diagnosis of what is, apparently, mild emphysema. And you have no symptoms that you are aware of....
I would like to add, I stopped smoking back in 1999 and I an 41 years old. I exercise a lot (ardio, core, yoga) and walk to and from work (30 minutes each way) everyday. I don't feel out of breath or winded from walking.
Thanks