My admittedly weak understanding is that there are 6 or 7 quite distinct major regional cuisines in China, each divided into a number of smaller cuisines associated with a particular city and that the American version is very loosely based on only one of them (as it existed over a century ago to boot) with some borrowing from other Chinese cuisines and a lot of substitution of more "Western/American" ingredients and flavors. It is "Chinese" in the sense that it was primarily originated by Chinese immigrants and their descendants and drew inspiration from food actually eaten in China.
Food ethnography is a fascinating and very complex subject with which I have only a passing acquaintance. Any country larger than say Lichtenstein usually has multiple regional cuisines, which can vary immensely. We talk about food from particular countries as if everyone from those countries ate the same thing, but just as a crude example, look at the difference between food from the north or south of Italy. Or New York vs Chicago (and it's more than just pizza), let alone New Orleans. But if I talk about Italian food, we probably have similar images in mind, no matter how technically inaccurate that label is.