> but rather by the electrons in the light-absorbing molecules of your rods & cones becoming spontaneously excited by ambient heat energy rather than absorption of a photon

Agree, it's not a digital system so there is always some noise, just like you can never get perfect silence in terms of sensory perception. Your brain has also a way to project some kind of images in your mind even when you don't see anything in complete darkness, so it's far from just being the detection of photons.