Sorry, I wasn't alive back then but the car does seem like a muscle car
to me. I saw two doors on the car when I did a websearch. A coupe tends
to be more sporty looking.

If you don't want to call it an American sportscar/musclecar, you can't
deny it's a big, heavy car with a typical American build for the time
period - heavy, big inefficient engine, sucks lots of gas. Of course
driving it fast won't make that much difference in mileage.

Now lets compare a modern car. Speed will make a difference in mileage
there.