We train for surface protocol to become automatic, so even depraved of oxygen, it becomes a reflex. It does a big difference, you'd be surprised to see how many ppl blackout when surfacing because they exhale too much first :/

Regarding Mifsud, he had a YouTube channel, in French, which is full of information about freediving ! He worked a lot with scientists to understand how his body work and how to reach this world record. Also he confessed that he does not have spams when holding breath, so it helps a bit.