The passenger cabin is the main focus for the temperature control. The cargo holds are not heated as such, but get the residual heat from the cabin above. That’s why your cases were cold. The very rear part of the rear cargo hold (on the 747,757,767,777 A330 & A340) is called the Bulk cargo bay. This bit IS heated and is were they put live cargo. (I had to explain this to a rep from a major drugs company who was concerned that his medicines were going to get too HOT!) They can switch the heat off to save fuel. This has led to a few canine ice lollies over the years when the crew forget!

Rgds Cking