Well, they do have a point insofar as a filled ice cube tray, left outdoors, would freeze. (This is Norway we're talking about here.) But, then again, to the extent that heat there is electric, any watt of heat that doesn't come out of a lightbulb or an appliance, comes out of the radiator instead, for the net result in zero savings of energy.
Can't freeze water outdoors since a bird might poop in it.
Or the birds and other animals might see the water reflecting and crash or drown trying to get a drink.
What about hibernation and birds flying south for winter, you ask?
What if a bird was detained at TSA and missed their flight? Rumor has it that they are , err... bird brains.
Why, if it only saves one sparrow or passenger pigeon ...