Hong Kong has maintained their own independent Olympic team since 1952. During the handover of the territory in 1997, China outlined in the treaty that incorporated Hong Kong and later the Hong Kong constitution in Article 151, Chapter 7 of the Basic Law,

May, on its own, maintain and develop relations and conclude and implement agreements with foreign states and regions and relevant international organizations in the appropriate fields, including the economic, trade, financial and monetary, shipping, communications, tourism, cultural and sports fields"

I really don’t get what’s so hard to understand here. At the Olympics, they are two separate entities with two separate Olympic committees.