As you said: a Peltier heat pump is a purely electrical device, so if you're using a broader definition of the term, it could be a variety of different types of devices.
But that is the introductory paragraph, the author is defining what they mean by "heat pump": a device for heating a house which is powered by electricity. You could power it with something else, but the point is to replace natural gas furnaces.
My mind parses the term "heat pump" as a device that works on temperature by compressing some medium. Works out just fine for most heat pumps, but not at all for e.g. the Peltier element which is about moving heat from one side to the oher ("pump") but does not involve compression at all.
But that is the introductory paragraph, the author is defining what they mean by "heat pump": a device for heating a house which is powered by electricity. You could power it with something else, but the point is to replace natural gas furnaces.