Yeah… I’m more inclined to say this isn’t canon, since every material referencing the tribes of bara magna does not mention an Earth Tribe, or a element lord of earth. I can not imagine this “Dark History” is anywhere near dark enough that it would make sense.
Furthermore even if Greg did confirm this at somepoint, it holds the same validity as that wave of nonsense canonization that Boidoh went on with Greg awhile back. There comes a point where it’s clear greg is just saying “Yeah sure, whatever keeps you people from asking me more question. Stars are definitely made of cheese in Bionicle”
I mean the fact it contradicts established canon is proof enough that even greg doesn’t seem to care that much and/or is able to keep track of what is and isn’t canon anymore, because people just don’t stop asking for meaningless things to be canonized.