Are immigrants from China still locals?

When you get a green card, you are just a permanent resident, which is commonly referred to as an immigrant. At this time, you are still a citizen of China, and you are still a China citizen with a China passport.

After several years of immigration, eligible people can apply for naturalization. At this time, your China passport will be invalid. Whether you come from China or not depends on what kind of passport you hold.

This is legal, isn't it from China?

In a moral sense

You are still from China, but not if your children were born abroad, because your children are totally foreigners without the influence of China culture, even though they have yellow skin.