Welcome to FT hanni
The AA agent you got was incorrect
call again and get a (hopefully) more knowledgeable agent
As Dave Noble pointed out (and you obviously already knew, given your plan to get from Noumea to Tahiti by other means) - the problem on a Oneworld Explorer is that there are no available flights westbound out of Tahiti; the Global Explorer allows travel on the QF codeshare on TN's flights PPT-AKL and AKL-PPT.
It should be worth booking through AA - to avoid some of the various fuel fines. BA and QF are just about the worst to book through for this.
Happy travels