True, but they didn't choose to leave it either. Britain had agreed 100 years earlier to return HK to China and kept its promise.
Really HK should have become independent, but no doubt China would still claim it as theirs.
Actually, the 100 year lease was only for the New Territories, which make up the bulk of Hong Kong's territory, but only about half its population; Hong Kong Island and Kowloon were fully annexed by Britain. However, Britain decided it couldn't sustain Hong Kong without the New Territories, and that's part of why it was returned to China at the same time.
Did they have even have a choice under Britain control? Nowadays at least you hear the voice
Yes, they were eventually self-governing under the British and were British citizens from 1904 onwards. Though it was a long and winding transition from a colony to a self-governing territory.