I'm guessing in their efforts to clear the snorkle they were swallowing saltwater. They had to blow out a big puff of air to clear it, so they needed more air quickly. They were anxious to get airflow started hoping for longevity. Had they known the way the challenge would turn out it might have been smarter just to stay under as long as they could without even trying to clear the snorkle. That said, I can't even sit here at my computer and try to hold my breath and make it very long, much less under that kind of pressure!