That is definitely known and calculated in. That is known from the map data. As a way to see that obviously, you can plot a trip, and then look at the Trip line graph in that energy app in the car, and it shows the line of remaining energy rising and falling in the opposite directions of the uphills and downhills, just as you would expect.
I'm pretty sure that is mostly wind. My wife and I were on a trip across I-80 in Wyoming once in our Toyota Prius, and it has that instantaneous mpg gauge. It sat there pegged at 99+ mpg for a very long time, as we had a really fierce tail wind. That can make a shocking difference sometimes.