Chong,
The nursery is definitely selling a plant with the same leaves and fruit as this, calling it "Java Plum (Duhat)":
http://www.tradewindsfruit.com/java_plum5.jpg
and the plant does not look like this:
http://www.stuartxchange.org/Duhat.jpg
So I thank cherokee_greg for bringing up the matter in the first place(!) and Chong for his knowledge of tropical fruits.