Now that looks quite well-fed. Imagining this animal being just about only half that... the miserableness straight jumps in your face from that sight.
Due to someone else around here on LJ being (or having been) faced with their cat needing to undergo chemo, and a quiet sign of the cancer being also losing weight (while the cat still showed a healthy appetite for her age), I'd throw in the guess maybe he had some sort of cancer too.
