Is weight loss necessarily determined by calories burnt?

I know you need to burn 3500 calories to lose one pound of fat. but when I eat one meal every two days, I can lose 11 pounds in 4 days. and the weight never comes back. this means I burned about 3500 x 11 calories in 4 days! but that is impossible because my resting metabolic rate is 1600 calories a day. So I want to know how this is possible that I lost 11 pounds in 4 days and the weight never came back.

Today I ate 600 calories. and will be drinking water, coffee and tea for the rest of the day. I do not plan on eating anything more. When I was at my heaviest (200 pounds) I could go 48 hours without food before I started to feel hungry.
Is weight loss necessarily determined by calories burnt?
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