difficult one
The press report does not mention whether the floats had been inflated or not. Neither it says whether the helicopter went upside down at any time during the event.
Given the shape of the aircraft and its CofG position, I think reasonable to assume that the floats have been inflated by the pilot, otherwise the a/c would have capsized almost immediately after landing in the water; especially if sea conditions were not completely calm. Even if the cabin has a good degree of water tightness, to exit the a/c the medical crew may have left the a/c by jettisoning the windows from the sliding doors and maybe the external water level was lower enough to prevent massive water inflow. The pilot, however, only had the choice to jettison the cockpit door in its entirety and the water would have flown in the a/c in a matter of seconds. If the floats had not been inflated, the aircraft would have most probably sunk almost immediately.
There is no mention of the life raft, which, in most recent floats configuration, is packed in the floats themselves, thus not requiring the crew to manually throw it outside of the cabin, when their main concern is to get themselves out of the cabin first.
The air trapped in various areas of the a/c (like for example the fuel tanks and the baggage bay) can help keeping the a/c afloat for a little bit, but not necessarily in its upright position.
As in any other accident I think that it is dangerous to make too much speculation on technical or human factors involved in the chain of events that led to the accident without knowing all the facts and the rescue of the helicopter will probably be necessary to clarify what happened.
I think we must be glad that the "system" overall worked fine and allowed the crew to be safely rescued in a very short amount of time.