It is a very interesting scenario, most of it seems feasible, but I think it is all really contingent upon whether the black hole would evaporate quickly or not, and from my very scarce understanding of black holes, Hawking radiation emission makes black holes decay over time, and smaller black holes emit Hawking radiation quickly enough to evaporate very fast. I'm not very sure exactly how size relates to speed of decay, but in general I think the smaller it is , the faster it is consumed. About the black hole in the core, it doesn't seem probable that it would stabilize as it would always be attracted to the matter around it, and there would probably be enough angular momentum in the earth's rotation and movement to make it collide with the surrounding matter.

While he is wrong in saying that we cannot create a black hole, there may be some truth in part of what he is saying. I think that the gravity of this very small amount of mass would not be capable of attracting enough other mass to be dangerous, even if it were technically a black hole, as the event horizon is proportional to its mass. Being a black hole doesn't affect its total gravity, if I understand correctly, but it may change the mass's behavior in some other way that makes it more able to attract other mass, I don't know.