The FATF report goes into it in more detail [0], but to put it very simply - Australia doesn't have the protections it should, when it comes to money laundering.
No. The linked article admits they're wildly guessing and links to another report with recommendations but no numbers I saw from a skim. I hear this repeated regularly on HN but am yet to see a reliable source beyond "but it's Chinese money".
In my empirical experience, its more to do with stashing the proceeds of state capture by politically connected individuals in China.