I think this is an excellent video with several lessons learned...and for now, putting aside anything they could have caught during preflight due to fuel contamination.
Obviously he executed a perfect water ditch, and since it was captured on video, we are lucky we can learn from that.
It is really hard to see people in the water, unless you are right on top of them. One of the best signaling devices you can own is a mirror to reflect the sun during the day, and a strobe during the night. Google "survival mirror" and you can get one from REI for less than $5. Simply waving at your rescue will not do. They will not see you. Chances are, they will fly right past you (assuming like in this case, there are no other debris in the water). Assuming a calm sea state like the one they were in, they could have splashed the water to make them stand out a little more. Not so much of course in rough seas with white caps all around. Reflective tape goes a long way if you have a raft. Had their friend not been orbiting overhead, I bet the Coast Guard would have had a really tough time finding them. Even worse if there was a strong current. It took the Coast Guard about 45mins to get to them. With a good current, you can drift a long way from where you ditched in that amount of time, and drastically expanding the search area for your rescue. They were lucky they were still within cellphone range.
Put the water temperature into your flight planning calculus (altitude/glide range) when you are going to transit over a large body of water. They were showing signs of hypothermia after 30 mins. Imagine if it was winter...or they were in the PNW.