I have a theory:
What if the Eridian Fabricator… is actually Butt Stallion? It would make sense for Handsome Jack to come across it, he seemed to have done a lot of research on eridians. Maybe Jack created the pony and installed the fabricator inside it. Then it somehow ended up with Typhon in the intervening years.
Or maybe… it has some kind of sentience and is able to take on different forms. It wants to keep a close eye on the events of the universe, and so during the events of BL2, it turned into a diamond pony to get close to Handsome Jack. After his fall, it sought out a new master.
There is absolutely no basis for this theory other than the fact that in Tiny Tina’s DLC, butt stallion also pooped out guns when you fed it eridium.