I met an academic from mainland China at this conference in Massachusetts (which has just finished). (This man barely spoke English, and he spent most of the conference talking only to other Mandarin speakers, so I’m not sure why they bothered coming.)
After spending ages trying to explain my work to him, naturally the question was asked as to where I was from. Cambridge, in the UK, of course. But where was I from originally? The UK. And so it continued; it was completely inconceivable to him that there would be ethnically-Chinese people who had never lived in the PRC or Singapore, and who don’t speak Mandarin.
This is by no means the first mainland Chinese person that I’ve met who thought along those lines.
‘Go back to where you came from’, and sometimes ‘Where are you originally from?’, have the implied message ‘you’re not really one of us’. These statements are now commonly recognised as forms of racial harassment. But the implied message ‘you should be one of us, not one of them’ is also based on the idea that a person’s identity is determined by their body features (such as skin colour), and can be just as effective in depriving a person of the rest of their identity.