Regarding the Plymouth incident, my information is that this 51 YO WM's immediate cause of death was drowning as a result of a accident while scuba diving. Now, that does not rule out a heart attack(or other medical emergency) underwater causing the man to become incapacitated/unconscious. He might then have inhaled enough water to cause drowning. In any event, he was discovered floating facedown in the water off a boat near the nuke plant. The folks on the boat brought the victim to the surface and found he was unresponsive. Subsequent CPR by civilians and medical personnel failed to revive him. I have no information regarding a dive buddy or group diving or any other specifics.
I would agree that, even though the official cause of death was drowning, this might be more acurately characterized as an accident and not a scuba diving accident. It wasn't like the man suffered a case of the bends from diving too deep, dove with bad equipment or pentrated a dangerous overhead environment unprepared, etc. It seems there's no 'lesson to be learned' from this diving death.
Keep the man and his family in your thoughts, he was a father, grandfather, reserve police officer and business owner.
LobstaMan