I am a US citizen in Hong Kong and would like to go to Beijing for 56 hours

and then fly back to Hong Kong. Do I qualify for the 72 hour visa free transit?

I am concerned about the below, according to Trip Advisor....
- You must be in transit to a third country (you may not return to the same country as the one that you came from);
Also noted:
You have confirmed plane tickets to a third country (for immigration purposes, Hong Kong, Macau and Taiwan are not considered part of China). Flights between mainland China and any of these places are considered International and they are deemed to be different countries;