I am not from China, but from Sinai. Is there a grammatical mistake?

There is something wrong with grammar!

1 is not preceded by the indefinite article a. China people! If you want to say "I'm from China", you can just say that I'm from China. There is no a .. According to my observation, it seems that all words ending in ese refer to which nationality, and the singular number does not add a; The word ending in an indicates which nationality, singular plus A. For example, I am from China. He is Japanese. She is Korean. He is an American. She is Canadian. And so on. . . . . . . . . . Please correct me if there is anything wrong.

Shall we invent a word to express the concept of "China people"? I remember this word should be Sinaean, which means the same as Chinese. You spell Sinaian, no wonder some people say it's Shi Naian, which makes a joke, hehe.

I think your original intention of saying this sentence may be based on your understanding of the suffix of Chinese. Because the suffix ese means "smaller, worse and less" in English, it contains the meaning of discrimination, contempt and contempt. You see, the word singular ending in ese can't have a, and the word singular ending in an can have a. Isn't this discrimination? There is also a homologous suffix ess, which means the same thing, so the word less means less difference. You see, Americans, Canadians and even Indians never say what they are or what they are. They like to end with -an There is a historical reason why the word "China people" was China-oriented. It is not easy to change it now. We can only rely on the constant strength of the people of China to give the word life a new meaning. I think that's what you mean when you say you are from Sinai. Sinaean ends with an, and when it is singular, it should be possible to have an in front. This is just my understanding.

So, I think the correct expression of your sentence should be:

I'm not from China, but from China.