It's because Conservatives use "true American" as a way to exclude minorities (especially non-English speaking minorities, such as Puerto Ricans) that Progressives make a big deal about how being American is a legal status, thus it is racist to deny people their "American Heritage", by which they just mean citizenship, based on "do they speak English".

However, then there's Chinese-Americans who take that logic and try to claim they should get cultural claim to being Chinese then get offended about "conservative racist Chinese" people who deny their "Chinese heritage". To which, of course, I wrote the entire entry.

Obviously, the other trigger is Americans trying to talk about "racism in China" and it's like...look, there's definitely ethnic tensions, but calling it racism isn't helping.