Earlier quoted context omitted.
The Prius gets up to 50 mpg on the highway too, much better than ICE cousins.
How is that possible? What's it doing that ICE cars can't do on a highway?
Hybrids use a smaller engine that is running in a more efficient operating range during cruising (i.e. not pulling a huge vacuum and moving lots of parts the whole time). The battery/motor comes in for acceleration.
Unlike combustion engines, electric stuff isn't really inefficient at low load.