Why "Peanut Sauce" is known as Thai Food while Thai people in Thailand don't know what it is?

Of course I am Thai, born and raised in Thailand.

I find it funny that "Peanut Sauce" is everywhere in the west and seems to get more popular. People always refer it as "Thai" and many believe Thai food is all about peanut.

If you go to Thailand, ask them about peanut sauce and most will go blank. They don't know what peanut sauce is.

Thais put ground peanuts, as just another ingredient, in so few dishes that they don't consider peanut a main ingredient of Thai cuisine. And peanuts are coarsely ground so that they're like thick grains of sand, and not mud or peanut butter.

Why is it like that?

A lot of things are like that. Thai restaurants in the US try to cater to the taste of Americans. Same for teriyaki restaurants. You won't find stand alone teriyaki restaurants in Japan. Or tacos and burritos aren't really considered Mexican food. If you order fettucini alfredo in Italy, people will laugh at you.

But hey, I love phad thai!

I suppose it was someones idea of "Americanized " Thai food-- their own creation, actually,--- was to use a peanut sauce. ( If I remember right , peanuts are native to the Americas and not Thailand).

I would say that it would be some kind of a "fusion" food ingredient. Fusion food is the unusuall blending of two foods , of different origins, like "Chinese Tacos", That might include bamboo shoots and water chesnut, and soy sauce inside a Mexican corn tortilla, with Guacamole on the side!.

you're right...but then chop suey is unknown to the chinese as well

In Australia peanut sauce (also known as satay sauce) is known as being Malasian or Chinese, certainly not Thai!