This is a case of the 1: 10 million chance. Nothing remotely suspect about it what so ever.
I do not think it can be assumed that all were in their cabins. If the storm was exceptional, some may have preferred to sit it out in the saloon, which was at deck level.
DH is a Naval Architect, a ship designer, althought we worked in the offshore industry. This boat was state of the art designed by someone who patented his first invention at 20. He was constantly pushing the limits of technology on these ships to reduce crew size and it was claimed this ship could be sailed by one man with a joystick.
DH says that often when you are pushing design like this, everything might look fine on a computer print out, but instinct tells you there could be dangers and where they might be. The problem with virtuoso designers is that they generally do not brook criticism or doubts.
The cause could be hubris, it could be a 'Black swan ' event that couldn't be forseen - like the wind spout, it could be material fatigue of some kind, or human error. DH refuses to commit himself until he has more information.