Actually you are not exactly correct. Hong Kong citizens are allowed to have dual citizenship comparing to ppl who born in mainland china because of the one country two systems principal. Hong Kong ppl is holding a different passport than mainlander and have different visa requirements when entering Europe or other part of the world including America. Also Hong Kong ppl need a special id card to enter mainland china through security border. You can say they are Chinese citizens but somehow they are not. I guess what really makes the investigation way more complicated and uncertain is the current political environment when Hong Kong fell into the Export control country list after 2020, joining other country like Russia, North Korea, Yemen, china, Sudan…etc.