A lot of debate over the source of the smoke (or whatever), but I join the crowd who consider it to be from the exhaust (for whatever reason). The floats inflate a fair bit afterwards, first starboard side and then (still later) port side. I remember some footage on YouTube years back of a US media helicopter making an emergency landing in a carpark while being filmed by another helo. It also released a hell of a lot of smoke, but not just for such a short time, rather all the way to the ground and after safe touchdown. The motion of the helicopter as it descends in this case looks somewhat irregular almost as if it is being acted on by a sling line under tension at some stages?? I have seen RC helicopters 'thrown around" like this, but never realised a full sized helicopter could also react this swiftly.