It's more an explanation of how you can have gas heat without power. Also, even heat pumps use a heating element at some point below 28~30 degrees. If you rely on the pump only below that, it'll start to freeze up into an ice block itself at some point.

Plus having a continuous plug-in (natural gas) fuel source is a big advantage over refilling a gasoline generator, which most portable generators are.

Heat pump efficiency drops a lot when the temperature goes significantly below zero celsius