...unlikely it is that an untrained passenger...
I think the training deficiency could be bigger than that as most of our tourists simply cannot swim. Then there is basic physics knowledge that most of them aren't aware that a helicopter is often top heavy and the consequences thereof. They probably even harbour false assumptions with landing on water.
It's not their fault, they probably only wanted to take a convenient short trip over water without needing to have a masters degree in what can go wrong.
Now when I sit as pax on a Boeing or Airbus and look at the emergency card depicting a fully intact airliner floating on water with all life rafts deployed.... I know of only one incident where it actually happened, further perpetuating the belief that it does exactly what it says on the card.