Not racist, people are just curious.
Since moving to Brisbane, in 12 months I've had half a dozen people comment that I can speak English so well, and that I must have been born here. When I lived in Sydney, I don't think I ever had anyone comment to me about how amazed they are that I speak English without an accent.
I find it odd to be asked this question so frequently (but not offended) and I am assuming that it's because Brisbane is less multicultural than in Sydney.
Most people can spot I'm Asian but harder to pinpoint which Asian country. I've had people of Chinese origin assume I am Vietnamese, and Filipinos assume that I am Korean, and I've also been asked if I am Japanese.
Throw my surname in the mix and I get asked if I'm Indian, German, Dutch .....even when I am standing in front of them.