Most autos run on what is correctly called a torsion spring: a coiled spring that is designed to store energy by winding tighter, and release it by unwinding. As opposed to what you usually think of as a spring, a coiled spring that expands axially (a compression spring).Philosophical question: is it still considered a coil spring if it’s just a round piece of spring that’s less than a complete coil? That might be the technicality that allows them to call it a torsion bar. Or, the fact that it neither expands or compresses in the sense that we normally associate with coil springs, but more winds and unwinds. Just throwing out guesses here - I’m by no means an expert in the springy sciences. Could be both are correct, depending on the shape of the spring.
Come to think of it, Kershaw calling the speed safe spring a torsion bar is also a misnomer, as a torsion bar is designed to twist, not bend.