The Aztec Empire was founded in 1428 by people who migrated from the north to the Valley of Mexico.
By your reasoning, the Aztecs should not be counted as the indigenous people of the Valley of Mexico. They certainly are considered as such.
Similarly, the Inuit in Greenland only got there after the Vikings. The Vikings died out, the Inuit stayed. Again, they are considered indigenous.
In all three cases- the Aztecs, the Inuit and the Maori, they had developed unique cultures. In the case of the Aztecs and the Maori, Europeans then arrived and destroyed those cultures.
I mean if you really want to be technical, the only place humans are indigenous is the East African Rift Valley.
I would also suggest you look at the second definition here: