I'd be interested to know what the LHS pax meant by 'retarded the throttle' - if he did in fact chop the throttle at 400' whilst trying to fly the aircraft from the wrong seat with a dead or dying pilot slumped over the controls, I'm amazed that any of them survived!
Having seen the results of a similar event and the fact they survived with the aircraft fairly intact, my guess he meant lower the collective and then when near the water either went full down or cut the throttle. There are a number of GOM pax out there that have a good basic understanding of what things do in the cockpit after flying to work for many years. The one thing I find amazing is this guy got the floats inflated as well. There's some CG video footage that shows the inverted aircraft hanging on the floats with the pax sitting on the belly. While it might have the pilot's day it certainly wasn't this guys day to hang it up.