>>543640735
It's on a peninsula that was completely cleared. The other sides of the factory were walled off. This attack happened a long time after that peninsula was cleared.

What I have to assume is that one spitter from a nest on the far left aggro'd away from its nest as I drove past to scout and then hid in the fog of war for several years until after I opened the top wall of the map. Then it wrapped all the way around to the miners specifically, ignoring the actually factory as it past.