You misread the history of HK. The city of Hong Kong comprises of three regions: the small Hong Kong Island, the Kowloon Pensinula and the much bigger New Territories. Only the HK Island is signed over to the British Empire in perpetuity. Kowloon and New Territories are leased for 99 years. So the British had to return those 2 regions back to China in 1997. The tiny HK island itself is too small and insufficient, in terms of resources and infrastructures, to become independent.Huh ? Hong Kong was a full blown British colony. It was transfered over to China in 1997 as part of a new treaty. Up until then it was not property of China at all even though China wanted to claim it for many many years since signing the original rights away to the British Empire after the British claimed it for themself.
"Britain occupied the island of Hong Kong on 25 January 1841 and used it as a military staging point. China was defeated and was forced to cede Hong Kong to Britain in the Treaty of Nanking signed on 29 August 1842. Hong Kong became a Crown Colony of the British Empire."
So the real outrage from Hong Kong should have come in 1997 yet they were Oh so happy to part ways with the British Empire. Now they are in for a future of real hurt brought to you by the Chinese, I shed no tears for them.
Before China's economic boom, Native HK peoples thought they were the elites and mainland Chinese were poor and uncivilised. Mainland Chinese speaks Mandarin. Hong Kong people speaks Cantonese, which is a dialect of the Chinese language, but not the same. So peoples from HK never wanted to be part of China because of cultural and other differences.