I wanted to say "calling it" but we know so little right now that I can't claim to be confident in this, but anyhow, I'm theorizing that the Toa came from the Ancient City or whatever-- like, they were sent up into space or wherever by the ancient Okoto society that made that the prophecy drawings that the village elders show us in the animations, or possibly by an even older group of Okotans. I just realized that's basically saying "I bet it's exactly like in the original Bionicle" but I forgot that's what they did the first time and I was thinking of something a lot less convoluted for this time 'round