Not exactly true. The body prioritizes based on need and what is available. Generally speaking, the body burns alcohol first, then other simple sugars, then complex carbohydrates, then proteins, then fats, and as a last resort the body uses muscle.

This is important to know if one wants to lose weight. Long sustained exercise will get the body to burn the available carb and protein calories and then start burning fat. Short intense exercise sessions never get to that fat burning stage unless the person is working out on an empty stomach and there are no available carb and protein calories to burn.