Heat is a spoiler. And it's amazing how much heat a hide will hold in, long after an animal is dead, even in freezing weather. A deer sized or larger animal will especially retain heat and start to spoil if it hasn't been opened up and had the innards removed, for a couple reasons. The first is mass. More mass, the longer heat is retained. Second, air circulation. The more air circulates in the chest and gut cavity, the faster heat is pulled from the body. Third when an animal dies, the process of spoiling or rotting begins immediately. Cooling reduces that process. But if the carcass stays warm and the spoiling process takes over, that process often creates it's own heat. Think of a compost pile. You will often see steam/heat coming from a compost pile if you dig into it on a frosty morning. Lastly, blood is the first thing that's going to spoil on a dead animal. One that was hit like this one has massive internal bleeding. That sits all night in a warm carcass, it can create a chain reaction that can spoil a lot of meat in a relatively short time.
