Some of the electric heaters are blowers (https://www.rwy.com/products-rwy/track-heaters-accessories/e...) while others use heating elements in direct contact with the tracks (https://spectruminfrared.com/railroad-products-and-track-swi...).

I suspect any of these mechanisms, however they work, are going to be wildly inefficient. The very premise of melting ice outside in the winter on big pieces of metal exposed to the elements seems like a huge energy sink. Whether electric heating is sufficiently more efficient to offset the inefficiencies in power generation and transmission I couldn't say, but it's far from clear to me that the 'American method' of using propane is crazy.