Well, we're never going to know, for the reasons given. Personally I was never short of breath even when I was a smoker, and I've certainly not felt that lung capacity was a constraint on my performance since I got back on the bike. Of course, for all I know I might have been Miguel Indurain in another, non-smoking, life.

In any event, there's more to aerobic fitness than just lung capacity. It's a whole-system thing.