Yeah lung capacity has a lot to do with it but as you gain in fitness you are also creating that capacity. More red blood cells, a higher surface area of papili in the lungs, etc.

The other thing is mental conditioning. In both freediving, and in cycling, you have to condition your mind to be comfortable with a lot of stress on the heart and lungs. And your mind has to be able to handle that feeling of not getting enough air and keep going.

Plus for those holding over 2 minutes it shows a higher than average lung capacity which they may, or may not be aware of and using on the road.

I was watching "Le Grande Bleu" the other night and decided to see how I did (off and on smoker, on right now) and I swung 2:21(Bah, 2:11, mistype)

One difference I would imagine is that holding your breath underwater you could probably go longer than doing it out of the water. When your in the water you have that whole 'drowning' thing to help you hold your breath longer. When your on the surface your body 'knows' that air is close and it wants to start breathing again that much harder.

I think one of the reasons I am not worse off than I am at my weight is my lung capacity.