Small helo used for towing = not smart
Considering that a Bell 206 barely has the power to lift itself and a few pax into the air, it suprises me that a pilot would be stupid enough to think that little 420 shp engine would lift the helicopter and 2 crew, and pull a 2-3,000 lb boat through the water (which adds drag) with another 3 people in it.
He probably could have done it, just not very fast. Put the helo into a hover, add just a little tension on the line, hover forward a bit and the boat would keep pace behind the boat. But that cowboy tried to fly off at high speed, and it's akin to a poodle running full bore towards a fire hydrant with a chain around it's neck....eventually the dog will feel an abrupt jerking motion that'll knock it onto it's arse.