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It's more of a turn of phrase, since you partially terraformed part of the planet, and only really explored a fragment of Trigaea/X'ir. Ash's progenitor crashed a fair distance from your progenitor, and the humans, x'irii, and machines are setting in a new post-terraform era, now their priorities have shifted.
Now you've terraformed a good chunk of the world you've explored and disrupted the societies, it's sort of like resetting your explorations back to near zero again.