Personally speaking, I think stand up paddle boarding is ridiculous. It has only got popular because it looks cool leaned up against a VW van on Instagram. A totally unsuitable craft to deal with even the slightest abnormal situation on the water....you might as well be on a Lilo. But I, like most members of this forum speak with the benefit of many years experience on the water and know how it can bite.
You can't expect people with no water experience to know this, and when they book a tour with a 'professional' outfit you don't expect them to lead you into a very dangerous situation and get you killed.
The assistant tour guide was killed when trying to rescue the people stuck, and the main tour leader and owner of the business was arrested a week later and charged with gross negligence manslaughter. It wasn't mentioned in the report as the MAIB only stick to the circumstances of the accident and don't directly apportion blame.....although they came as close as I've seen to doing so on this occasion.