But he said they don't know what happened under water. So, at this point it seems we know as much as the lawyer. Which appears to be not much. An instructor with team members were on a dive with the boy. That's about it. Everything else in this thread so far is speculation.
But they do know what happened underwater: the instructor was somehow separated from the victim. And that's the only relevant issue. Why did it happen? Doesn't matter, because there is no explanation (poor visibility? strong current? too many distractions?) that will absolve the instructor of their responsibility.