It's an air conditioned unit. Chills a can nicely, but clearly doesn't keep chocolate from melting, although I guess had the engine been running all day and I hadn't left it in there, it may well have worked
It's not - it just happens that the ducting for the rear vents runs beneath it, which has the side effect of making it feel a bit colder. Hence why the chocolate still melts!
It's no more an air conditioned compartment than the boot is heated because the exhaust runs under it