Could light/occasional smoking strengthen the lungs?
From your examples only the first is really true. Exercise leads to better physical abilities (within some boundaries).

Sunlight on the other hand is always potentially dangerous, depending on the dose. But the damages accumulate over the years which finally lead to the so called senile lentigos (others call them aging spots) occuring in sun exposed skin from the age of 50.

And the same is true for cigarette smoke. Here you expose yourself to a nasty cocktail of potentially harmful to cancerogenous substances (tar, polycyclic aromatic hydrocarbons, benzene, nicotine and much more). These do potential harm to your lungs depending on the dose (meaning how many cigarettes you smoke a day), but there is nothing like a harmless amount. Your lungs will eventually recover from this (tar takes the longest to be removed), but it is definitely not good.