Otherwise its, a bit like saying Jersey is not part of the UK.
Jersey is categorically not part of the UK, it's a crown dependency like Guernsey, Sark and the Isle of Man.
Hong Kong is a Chinese territory but is seperate administrative region from the mainland. Even the civil registrations remain non numerical, and travel between the two is not straightforward.
It's not a difficult detail to grasp surely? Hong Kong is of course not part of this ******* bilateral which in terms of aviation and geopolitics is a guide.