Exactly. Heat pumps work by concentrating and moving heat, which is cheaper than generating it in the first place. There's still heat in 0°F weather if you concentrate it.
I believe this was from a XKCD What If? question, it was asking how much would sticking a toaster into a freezer effect it? The answer was not much because the toaster heats up to 500F, so from a toasters perspective everywhere is cold and it wouldn't notice much difference from being in 70F or 0F. I remember this when talking about heat pumps since to refrigerant most places would be hot.
