Skeletal muscle is one of the major storage units for glycogen, which is formed from glucose. Although glycogen can be readily accessed to provide energy, the body's cells can become over-saturated and any excess is channeled toward fat stores. Essentially, the amount of glycogen already stored is the main factor that decides the fate of those additional carbohydrates. One way to control glucose levels and the associated probability of fat storage is to avoid a high-carb intake later in the evening. While total calories are most important in the fate of body fat levels, lowering glucose levels by avoiding late-night meals may also play a role.
Foods consumed later at night have a greater tendency to be stored as fat for two reasons.
First, you're less active at night, so calorie expenditure is lower. If you train earlier in the day, stick with a larger post-training meal, but make your final meal of the day lower in total calories as well as in carbohydrate intake. Typically, the quantity of insulin produced is in response to the amount of carbohydrate foods ingested. Based on this information, I'll speculate that a lean and muscular person can remain lean yet enjoy the luxury of occasionally eating high-sugar foods or carbs close to bedtime. This may be due to the body releasing less insulin and that the muscle receptors for insulin may be more active and sensitive than the fat-cell receptors for insulin.