can I use this policy to see Hong Kong on my trip through China?

I am on a trip through China and my flight back home is from Shanghai. I was wondering whether it is possible to visit Hong Kong (I.e. exit PRC) and then fly to Shanghai from Hong Kong, visit Shanghai for three days and fly home (to Austria). So my transit would be Hong Kong- Shanghai - Austria.

Issue could be that the flight back is actually part of a return ticket Austria - Beijing, Shanghai - Austria.

Glad about any help!

Cheers,
Markus