At it's core, yes, but I think it's less "cold air" and more thermally equilibrating with the radiative temperature of the night sky which is more like 3 degree

At it's core, yes, but I think it's less "cold air" and more thermally equilibrating with the radiative temperature of the night sky which is more like 3 degrees Kelvin. So in essence you are lowering the temperature of the cold sink until the ambient temperature is comparatively hot to extract work out of your heat pump.