This is such thing. How do you think Singkies and Hongkies were classified and travelled when under colony. It was colonial citizenship passport. The country name on the passport was British. All international rights as if British passport except no right claim British citizenship in Britain. That had to be applied for in another process. Many Hongkies kept those passports as long as possible after 1997. But after expired, the British wouldn't renew for them anymore except those successfully applied for British citzienship. So they look for other passports as HK SAR passports were new and weak. Singapore was obviously the best choice for them.