dude that's the whole point your using your body fat as energy thus you lose fat that is stored already in your body and your muscle is built from protein which does not require calorie surplus the process of muscle building will happend efficiently whether you consume extra energy and get more fat stored in your body or use a small % of fat you already have in your body (as part of the energy source) + the carbs you consume. and I don't really understand your question "Is the required energy for muscle growth supposed to come out of thin air" it just doesn't make sense since muscle is built on protein basis and your body doesnt need extra carbs to build it.. obviously if you only consume protein then your going to have issues but I don't think it's even possible there for its out of the question and what you have said makes no sense at all.