if he knows what he was doing with his nutrient ratio's he is eating plenty.
most people eat way too much carbs, way too often.
yes, carbohydrates are ABSOLUTELY VITAL to building muscle. BUT, there are only needed at certain times. First thing in the morning, pre-training, post training. Other than that you have no use for carbohydrates. They DO NOT build muscle, they provide energy for a workout, can help put the body into an anabolic state quickly, and post training help with the uptake of proteins into the muscle. so...assuming that you need no more than 60 grams of carbs in the morning, and 60 grams post training..and maximum 100 grams pre-training...thats a maximum real need of only 880 calories. leaving almost 3000 calories for proteins. assuming that he will be also consuming some healthy fats...lets make that 2700 calories of protein. So, eating 3800 calories would allow for protein intake of up to 700 or so grams of protein... which is an absolutely crazy amount of protein to eat.
sorry for stating the obvious here guys...but alot of posts talked about that being a small amount of food. its definitely alot of food if your eating right.
if your eating wrong, it could just be a half dozen jamba juices.