In his early 30s he started smoking at a time of real stress in his life. He never smoked much, about a pack a week, but sometime in there his asthma went away. We have no idea what happened because not much else had changed in his life. He lives and works on a farm in the house he was born in, the same things grow year after year, there is no obvious explanation unless you think about the smoking. BTW, he did stop smoking a couple of years ago and the asthma didn't return but he does get my second-hand smoke.
I'm not seriously championing trying smoking to cure asthma, it could have been anything, but as far as the asthma went the cigs didn't seem to harm.
Asthmatics today who do smoke are strongly advised to quit.
As for your husband's asthma, it is very common for childhood asthmatics to "outgrow" their asthma as they grow older without any specific treatment or change in environment or medication. It's just one of those things commonly observed that has no good medical explanation. On the other hand, there are some cases of asthma that begin in adulthood.