It may not be appropriate or fair to compare the visa-free figures given by the British Govt and the HKSAR govt. Their figures (virtually, anything claimed by any govt) are often questionable.
I would like to encourage you to read the Wikipedia article above. In fact, even the UK Govt does not include the country into their BN(O) visa-free list, many countries do grant visa-free for BN(O)s and BCs in reality. This can be verified by the IATA travel database, which used by airlines to ensure travellers have the appropriate visa before boarding. The IATA database has taken account of the differences of the six categories of British nationals.