It's psychosomatic. MSG is also in tomatoes, mushrooms, and tons of savory salted snacks such as Doritos. None of those tend to trigger the symptoms people claim to have after eating Chinese food.

dim sum is called dim sum though, you wouldn't expect to get dim sum except at brunch/lunch time and if someone says they are going to get Chinese food it'd be a surprise to get dim sum. Even traditional Chinese restaurants that cater to Chinese people serve Americanized Chinese food. In the Seattle Chinatown there's restaurants that have Chinese only menus that don't have any of the same stuff as the English menu. I've been to them with Chinese speakers and it's a totally different experience then going there with just my wife.

my original point is that "Chinese food" to most of the western world is the stuff that American Chinese immigrants invented. Real Chinese food isn't called Chinese food because China is massive and they have so many food cultures that those cultures are what that style of food is called