ccCapt is right on. There are many many species of nepthea. One is considered extinct, and others are considered endangered. Like he said too, if you get a green nepthia, it's impossible to tell what species you have exactly. You will have no idea if it's one of the extinct, endangered or totally common ones. They are pretty much indistinguishable by the eye, and their differences are at the molecular level. So good luck telling them apart unless you work in a biology lab!
I think that website selling them as "extinct in the wild" probably has no way to back that claim up. How do they know that's the one? It could be any of a hundred other species instead.
Kenya trees look similar, but are a different color than neptheas. They are related, but are by no means rare.