“They abandoned it all,”
Yes, but you are changing things. You said it had to be done due to a lease expiring which was not true.
“.. returning it to China.”
This is also a false statement.
They returned nothing to the PRC.
Return is a misnomer and false statement.
You appear confused. All of these lands were and are Chinese. The folks their might fly an American flag but are not now, have never been, and hopefully will never be American citizens. Nor are they now or at any time in the past UK citizens. No, the are Chinese citizens, the territories or lands or whatever are Chinese. Deal with it.