I didn’t see anything mysterious about it. It was known nearly immediately this guy had Alzheimers and finding them in separate rooms is certainly not uncommon.
The only odd thing is he had plenty of money to have an aid come by once per day or whatever. Then again some people like to live the recluse life and be hermits. They want to be LTF alone. I have no problem that either.
You left out the dog and you forget that at first most everyone looked at it and guessed carbon monoxide poisoning, which was a pretty reasonable guess with the first small list of details.