Slight digression, but I also do think this is an extremely good case for a trusted and global blockchain implementation involving testing labs, licensed hospitals / doctors, immigration authorities and in general public health related organisations.
Simple globalisation of important items like immunisations records, public safety related medical records etc should / can be implemented. Would be far more beneficial to humanity than say ... bitcoin.
Given the HK government trusts a local government chop more than a standard national government domain name registry I wouldn't hold my breath for them recognizing blockchain, even if every other country did!
From what I gather, the tests are not very accurate. There are people in hospitals with the virus and they get positive and negative tests on alternative days.
The PCR nucleic acid tests the HK government insists we all take are the most accurate kind available now. More accurate than the spit tests people take on arrival in HK or which seem will be used for the "widespread" testing of the city. More accurate than "rapid" antigen tests, which is why it's a challenge for anyone trying to get a flight for a "high risk country" to get them done in 72 hours before flight. And all the endless documentation requirements supposedly assure that the lab doing them knows what it's doing.
That said, if the test results are forged, none of that matters.