The point as I would see it was training for future landings on small beaches, gravel bars etc. this is were you initially land on the water and run up to your short hard landing area using the water to provide a breaking action, a perfectly normal manoeuvre.
Don't buy that. You just wouldn't do that in the middle of a deep cold lake. Landing in the last part of a stream before dry land or a small beach is a normal manouvre but that has zero to do with what they were doing there.
Won't do light aviation in the Lakes any good at all that.