I think it's recently been proven that the every 2-3 hours thing isn't optimal at all. Something about the decreased insulin sensitivity due to constant influx of nutrients (kind of like building up an immunity).
Most of the top experts I read recommend 3-4 large meals a day scheduled around workout times. (1 Pre-WO, 2-3 PWO)
Also, it depends on how he's eating at 400g/day. If he's doing a paleo-esque diet, I would think it'd be fairly normal if you're a large guy.
Carbs, from what i understand, are protein sparing - meaning the more of them you ingest the less protein you need to eat to increase muscle size.
I personally, while dieting, eat about 225pro/150-200carbs/70fat and while maintaining the only thing that will go up is the carbs/fat slightly
Carbs are protein sparing but they're also fat sparing. Basically when you have a diet high in carbs the oxidatrion of fat is inhibited and the storage promoted, mainly because of the effect insulin has. On the other hand, a high fat/high protein diet spares protein because when your body is adjusted, you require less glucose as ketones become the main fuel for the brain, and fatty acids the muscles. Less glucose = less protein breakdown to synthesise more glucose. Obviously carbs have their place in training though saying all this, but on a cut I don't see much need for them.
Glycogen is required for high intensity exercises, so if you're not doing heavy lifting/anaerobic training they aren't necessarily obviously.
But, as a physique-oriented person, glycogen/water makes up what.. like 20% of muscle size? I wouldn't like that one bit.
The carbs I take in while cutting are simply so I don't have to eat more protein (cost wise) and I also enjoy carbs quite immensely so it keeps me sane.
I also lift 5 days/wk and without 150-200g carbs a day I'd quickly be glycogen depleted which would hinder my performance (Which, keeping intensity at the same level, is how you limit muscle loss.)
Also, contrary to what people have heard about eating a high fat diet - eating high fat does not make the body burn more fat than it would by simply going low fat/carb - high protein.