Glad nobody got hurt or killed. Being an avid waterfowler, and having investigated numerous boating accidents, I too can understand how this happened.
Although if the incident had been a reportable accident, and investigated- the owner/operator of the boat could have been cited/charged with operating the boat beyond rated capacity(horse power and weight). However; that only had a minor contributory role in the incident. Most likely cause was the operators unfamiliarity with the controls of the Mercury Engine. I've several thousand hours operating these engines and own a 1984 mod. 18hp Merc. They are wonderful motors but can be a challenge to the un-initiated.
We have a young officer who picked up the nickname of "Flipper" at the academy. During a boat EVOC course, he threw himself out of the boat and managed to get back in the boat with only one instructor witnessing the "falling overboard" Most just noticed that suddenly he came back to the dock -"WET"!
Waterfowling is the most dangerous hunting activity from a casualty standpoint. The combination of Boats, water, and cold temperatures combine to make a potentially lethal combination. I've investigated three capsizings (involving waterfowlers) that were fatal. All fatalities were the result of "hypothermia" resulting in drowings. One was not a drowning as the victim was wearing a life-jacket (PFD)but succombed to hypothermia, and that in Georgia, not a really cold winter weather state.
When boating/waterfowling, it is impossible to be too careful
Good Hunting !!! And be careful out there !!!!