No. It's not like that at all. You keep repeating these false arguments.
Hong Kong was part of China from 200BC until 1842, so that's 2000 years.
Then, for the relatively short time of 99 years, they were a British colony, until they returned once again to China.
The Dutch don't consider themselves German because, unlike Hong Kong, they weren't part of Germany for all but a brief time in a 2200 year history.
Hong Kongers irrationally don't consider themselves Chinese, even though their origin is Chinese, and they've been part of China for 95% of the time they've existed. This isn't comparable in any way to distinct European countries.
Because modern "Chinese" population is bastardized with northern nomadic genes. HKgers, and Cantonese in general, have a different "Southern" culture. It's like asking why the Dutch don't consider themselves German. The Liangguang area should have seceded a long time ago like us Vietnamese did.