Bummer!

Well, give this a shot (let's rule something else out, shall we?) - take a succession of bracketed images from clearly overexposed to clearly underexposed, in 1/3rd stop increments of shutter speed while maintaining the same aperture. Get a complete tonal change example. Pick something static like the shot above, and use a tripod. I would actually call that one underexposed - and it's also where noise gets more pronounced.

Underexposure is devastating in video, which is where digital photography got its starting ground, and still shares some like-traits in that respect.

Get them back into Photoshop and see if there's any difference based on exposure.

Good luck!
-Lew ;-)