Presumably at some point long ago, Species-X seeded the cosmos with some form of AI Survey/Construction probes designed to locate and colonize resource rich planets, preparing the way for subsequent colonizing fleets. As such, it carries designs for a variety of mechanical "species": comm, constructor, overseer, resource locator/retriever, etc.
Once an initial city was completed, Species-X would be signaled and work would commence on maintenance and expansion until Species-X arrived with further instructions. However the number of successful start-ups far exceeded what Species-X ultimately used; reason unknown.
Over eons, accumulating data errors from radiation, circumstantial effects, copy errors, etc resulted in unit-mutation, eventually giving rise to evolutionary variance among the robotic breeds, with some types ultimately developing true Sentience and eventually your player species.
Its doubtful the mechanical races have ANY knowledge regarding Species-X since there is little reason for the initial probes to contain such information;; especially considering Species-X has likely either died-out or themselves evolved far beyond caring about what happened to their undiscovered colonies -- giving full freedom to develop internal mythos/etc regarding their presumed gods/etc.
Likewise there are potentially other such techno-worlds/species scattered among the stars given sufficient number of seed probes.
