It is hard to know what to say--definately this was an error. The report also noted that alcohol was involved. Such as shame that lives were lost! However, if they had had an EPIRB the lives could have been saved--even with the mistake of trying to pull the anchor. A hundred hours is not much time--and it notes no practical or formal education. The Florida on line boating safety course clearly states: "Never anchor from the stern as this can cause the boat to swamp. The square stern may be hit by waves, and water will splash into the boat. The motor's weight will add to this problem."
My post on another forum reminded me that I suggest that you secure the end of a chain or heavy line in an anchor locker with a number of passes of light line--in a C Dory perhaps 1/8" to 1/4". Multiple passes of light line from a pad eye to the last link will allow chain or the bitter end of the anchor rode to come to the deck and be severed with a quick swipe of a sharp knife. Cutting 1/2" or thicker line is difficult and take time--which can be valuable if you have to get out of a place, by cutting the anchor free.