One way to interpret this might be to say that metaphysics could, in principle, discuss the realms of what is merely "possible", as well as those things and facts that are "actual".
We can speak of things that are actually the case, but we also seem to be able to speak of alternative possibilities. I'm not actually throwing this laptop I'm typing on, but I could describe a scenario in which if I were to throw it, what sort of trajectory it might follow and what might happen upon contact with the ground. (it's quite a resilient laptop, but I imagine the force with which I throw it might potentially test its durability)
What kind of cognitive technology am I relying on in order to talk about counterfactuals? This would bring us into discussions about Modality, and there is a nice introductory Internet Encyclopedia of Philosophy article here on the subject.