Reminds me of this: https://io9.gizmodo.com/i-fooled-millions-into-thinking-choc...
And suppose further that 9 of them are still alive when I pull them out of the water. Not only are they alive, they are conscious, alert, and show no ill effects from 20 minutes underwater.
That would be a study worth talking about despite the sample size and lack of control and short time span.
Those would not be a fatal problems because we already know a lot about what happens to humans in general who spend 20 minutes without diving equipment underwater. We have a good idea of what the probability is for a human to survive such a thing, and can estimate the probability that my sample included 9 such people. It would be close to zero. Heck, even if I had the misfortune of accidentally getting my sample at a free diving competition the chances that I'd get 9 people who could hold their breaths for 20 minutes would be very low.
That's what lies at the start of almost all knowledge in science.
Maybe participants refused to stand more?