Whilst white Australia would at the moment probably like to exclude all Chinese, that would be blatantly racist, however practical and sensible it may be. It would never float.
So by allowing Citizens and Permanent Residents to enter Australia, regardless of whether they are of Chinese descent, prevents any accusations of racism.
What is ironic is that the Aust Govt has put in place tentative rescue plans for these almost entirely 'Chinese Australians' and their kids, but now they are complaining about having to spend 14 days at Christmas Island.
One of them whinged further in the press saying if it was a white Australian, they wouldn't be sending them there. Typical blinkered victim approach! I hope somebody pointed out that all rescued folk, be they Chinese, White or Magenta are going to get the 2 week quarantine. So what if it's a refugee camp, and how about just saying thank you.