Another battery question

[VanFan]

Hi All. I had my GC600 fridge turned on. Drove to my destination. Did not turn the fridge off directly but turned the red switch off. The next day-ish later, the battery is at 0%. I thought that the red switch stopped power going from the leisure battery, ie nothing would work. Am I wrong? Why would it drain? Battery is usually completely fine. Thanks in advance.