In a related concept, there are many divers that think that "smokers" can be good at using little air....that it is somehow an advantage to smoke.
I think it far more likely, that the cardio power is so low with smokers, that they are forced to use almost no exertion, and so swim slowly and carefully enough to stay within their drastically reduced aerobic abilities.....they end up using less air than many non-smoking divers, only because they absolutely do less muscle work--they have no choice.
If a situation comes up when the smokers need lots of cardio power, they will fail....having to help a diver in trouble, having to fight a big current, etc.
A very muscular and aerobic athlete that is so excited on a dive, that a large percentage of the muscle mass is constantly working/contracting, will waste lots of air....A very muscular and aerobic athlete that has become a good diver, will relax all non-essential muscles, and the pace of normal divers will be so easy for the athlete's muscles, this will be almost like absolute rest--and the pulse rate can be well below 70 bpm, with air consumption very low.