OK I am not a helicopter pilot but is it possible that having filled the water bucket they had the engine failure at close to max weight (assumption) which I guess means that they cannot hold the hover on one engine. The release handle is pulled and nothing happens. Now they settle into a low hover above the bucket which is visible on the surface and no longer affecting the weight of the aircraft. They can hold the hover but not go anywhere so surely the least risky option is to pop the floats out and land on, swim to shore and recover the un broken helicopter later.
Pure speculation of course, unacceptable to many I know and I shall now duck under the keyboard