Yup, as everyone already said, it's that the typical chinese american meal (or even a succulent aussie one) is a relatively well rounded one in terms of fiber and fats.
While you may or may not have been backed up a little, a decently built meal will go through in eight to ten hours, slide out easy, have good bulk, and also shove anything ahead of it out the door.
To maximize that effect, you want a balance of soluble and insoluble fiber (like rice alongside cabbage or broccoli, as examples). Soluble fiber holds water well, increasing bulk and helping things stay controlled. Insoluble doesn't hold water, and is thus a nice accelerant. Too much soluble, and things can get backed up a little; too much insoluble and it all comes out like a nightmare salad dressed with crap and sewage.
Fats wise, you don't want things greasy, but you do want it to be present in testable levels. Fats lube you up from the top down (unlike Fats, the big bear bartender at the club that lubes your bottom before going up you). It helps the digested matter slide through. Too little, and things can be difficult to get around corners; too much and imagine the pea soup scene from The Exorcist, only it's your ass and the soup is filled with diced carrots and tomato skins.
Chinese food, be it actual Chinese cuisine, or Chinese diaspora variants, tends to be relatively well balanced. Not as well as the prototypical Mediterranean diet, but in terms of bowel motility and excretion, it does well