Black Museum has loads of call backs to other episodes apparently. I'm still not sure about the Metalhead dogs, they seemed to target humans and I can't imagine a security system would go to the lengths they did. Possibly a military application that went berserk. I don't always need backstory but this one is a little frustrating because I don't see those dogs being dangerous enough to wipe out humanity. One wounded, poorly armed human was able to outwit/destroy one of them. In my head cannon there'd been some other cataclysm and the dogs were just a by-product.