Did not know that, but I think I like that more. Similar to Dune in which its setting doesn't have (human level conscience) aliens but humanity fucked with genetics so hard you'll find mutants that are borderline indistinguishable from what we would call aliens. That being said, Hivers
are aliens by
definition, just not extraterrestrial.
Unless they were made off planet assuming the all-powerful Second Empire at least went to the other two celestial bodies (which they most likely did given the wreckage you see around the world, their internal names, and other things such as the eye(s)), made labs like they did on the planet we play on, and then either brought them over or they arrived through other means (during or after the collapse of the empire, some may have stolen ships, and now there's Hivers and potentially other things that may have not been native to the world of Kenshi).
Then they would be extraterrestrial
and would explain why there's not much lore regarding the Hiver's origins. Reminds me of TvTrope's "
Absent aliens."