According to this: A last resort? - Summary Guide: The facts about immigration detention in Australia | Australian Human Rights Commission the top three countries of origin for arrivals at Nauru Detention Centre are Fiji, Indonesia and Sri Lanka.
That's awfully dated. Covers only 1999 to 2003.... And it conflicts with itself in several places. Like in the places of origin that you quoted. Elsewhere in the statement you find.
Most of the children in detention over the Inquiry period were from Iraq, Afghanistan, Iran, the Palestinian Territories and Sri Lanka.
that quote applies to ALL the OFF-SHORE detention facilities, while the one you used was for Nauru specifically.
A lot has changed in the world since 2003 --- so no one in this thread actually KNOWS...