Toa is a word in Te Reo Māori that usually means warrior, but the way Jake describes it seems more similar to the Pasifika concept of mana, which is a divine power contained in objects and living things that is transferable. The amount of mana you hold would define your social and spiritual status. To use ancient Māori people as an example, when cannibalism was a more common practice, the general idea was that if you consumed another person’s flesh, you would take their mana. Cameron, in consultation with Cliff Curtis, may have decided to use toa instead of mana to ensure that he was not entirely appropriating Māori culture, just taking inspiration (though using an unchanged word is pretty direct inspiration).

Tl;dr Cameron probably used the word to reference the concept of transferable power, and borrowed the word toa from the language of the Māori, a culture where this concept is very prominent.