"A current difference is that anyone who has visited or transited through a high-risk country must submit a recent covid test before boarding a flight to HK."
According to the Government website setting out the rules for travellers from High-Risk Countries,
"A person who is in transit in Hong Kong, and a person exempted by the Chief Secretary for Administration from compulsory quarantine under section 4(1) of either the Compulsory Quarantine of Certain Persons Arriving at Hong Kong Regulation (Cap. 599C) or Compulsory Quarantine of Persons Arriving at Hong Kong from Foreign Places Regulation (Cap. 599E) will not be affected."
https://www.coronavirus.gov.hk/eng/h...sk-places.html