Identify this unusually-shaped, orange-colored fruit that grows in pairs?
The seed pods reminded me of the Apocynaceae, so I searched for "apocynaceae china" and found this University of Hawaii page where it is identified as Stemmadenia litoralis.  However, a little more looking it seems Tabernaemontana litoralis may be the preferred name.  There is some debate here.  This book may hold the final answer regarding the genus.

Your picture of the fruit is one of the best one I could find on the internet. There is another good one here with other pictures of the plant.

You were also correct that as a planted tree it might not be native.  This plant comes from Central America.