Hawaii probably also works as an Exploration Age civ because they want to do Hawaii>America. There most likely won't be a New Zealand for Maori to go into so they could easily be Modern.It seems that Haʻamonga ʻa Maui was seen as an Antiquity wonder. While it seems that Tonga will not be in the base game, the inclusion of its wonder strongly suggests that it will be included later. And Maori also works as a Modern Oceanian civ, but I agree that Hawaii would work much better.
Other factors are that the Maori were the last of the Polynesians to discover their islands and they are the largest population group today.