I also noticed the water in the cave. The reflections are too mirror-like to me even though it's being viewed at such a grazing angle. Water should have some roughness to it and doesn't reflect light in a mirror direction for every photon hitting it. This leads me to believe that water material isn't physically plausible or they saved some GPU cycles by doing a mirror reflection to avoid re-rendering the scene just to add a roughness blur to the reflection and projecting it back onto the surface.
I know I fell for bait again. I know. But I can't stop.
I see your paragraph of theorizing, and I'll raise you more photo evidence, taken from life: