Brian Shaw is also 6'8" and 400lbs of muscle and he didnt get there by eating 10k calories a day, he stays there by eating 10k calories.

Muscle is metobolcially active, about 20cals a day, so if (subtracting bone, organs, etc) he's 280lbs of muscle, 5,600 calories is literally just to keep is muscle from melting away.

He also exercises as a job, probably close to 2k cals a day.

You need about 1200kcal a day for metabolic function.

So he's burning ~ 8k calories a day, the 10k calories is also when he's bulking up so he's trying to put on size both fat and muscle tissure that already exists (it can take years to build 20lbs of muscle, but lose it and try and put it back on and you can do it in months).

Tldr: You do not need to eat absurd amounts of calories to out on muscle, just aim for ~200 calories a day more than your maintenance. Eating 5k calories a day when you are 5'9" and 170lbs at 20% body fat will not magically make you put on lbs and lbs of muscle a month.