The body’s reduced metabolic rate in cold conditions. Exposure to cold water reduces the body’s metabolic rate — the rate at which it consumes oxygen and produces CO2. A person who is cold and largely stationary consumes less oxygen and produces less CO2 than a person who is warm and active. Okene was cold, and he was largely stationary. This metabolic reduction would have extended the survivability window.
The specific geometry of the trapped space. The orientation of the air pocket — its size, the position of the waterline, the degree to which the space was sealed versus partially open to seawater circulation — affected how the air quality evolved over time. A smaller, more completely sealed space would see faster CO2 accumulation and faster O2 depletion; a larger or more partially open space might see slower changes. The exact geometry of Okene’s pocket was not measured.
What the scientific analysis establishes, in combination, is that the survival was not physically impossible — which is to say, it was not a violation of the laws of physics. It was a set of conditions that happened to fall within the range that human physiology can tolerate, maintained for a duration that fell within the window that the physics allowed. It was extremely unlikely. It was not miraculous in the sense of requiring the suspension of physical law.
This is not a diminishment of what happened. The extremely unlikely is still extraordinary. The fact that the air lasted, that the cold did not kill him, that the CO2 did not reach toxic levels before the divers arrived — all of these are facts that could have resolved differently, with different conditions on any of the relevant variables, and the outcome would have been different.