Why is the Australian dollar, often viewed by traders as a proxy for the Chinese economy? The Australian dollar, often viewed by traders as a proxy for the
  Chinese economy, gained 0.3 per cent against its US counterpart.


From: S&amp;P 500 hits one-month high on renewed trade hopes (September 5, 2019)
I couldn't read the FT article... but...

According to this article here, China imports a lot of raw material from Australia. This means that if Chinese economy is doing well, they import a lot of stuff from Australia... hence AUD will appreciate.

This news piece, for example, says that as China is hit with new tariffs, AUD falls. This is because the Chinese won't be able to export as much, which means they won't demand as much raw material from Australia anymore.

Or this more recent article says that Chinese CPI comes out higher than expected. This means that it's more likely that the PBOC (China's central bank) will need to do something to reign in inflation, slowing down the Chinese economy and Australian exports. This depreciates AUD.