CUKC does not equal to BDTC.
According to section 11 (1) of the British Nationality Act 1981, a CUKC with the right of abode in the UK would become a British Citizen when the Act came into force in 1983.
https://www.legislation.gov.uk/ukpga/1981/61
For most CUKC passport holders in Hong Kong, this means that most of them did not become British Citizens when the Act came into force.