I think I've heard that float planes aren't supposed land in open ocean but under the circumstances would such a thing have been possible ?
"Supposed to...." is simply the water conditions. I have landed a number of floatplanes in the ocean - in very calm water conditions. Open ocean conditions would most likely be too much for even a Twin Otter amphibian, during most common ocean conditions, particularly if it's a very heavy weight landing, and unusually urgent. And if (though I expect not, with good cockpit discipline and checklist use) an amphibian's wheels were down for a water landing, it's a certain overturn in the water. I'm not saying at all that that was a factor in this case, just an important consideration for every amphibian.