It's just a handy reference for energy usage, and I assume this figure is more readily available due to the car being battery powered. It's a bit harder to work out for an ICE-powered car, as you'd have to calculate the energy required to move the car based on aerodynamics and weight. I have no interest in TSLA stock, nor do I think Tesla is anything like the sustainable future of transportation. I mostly picked Telsa because it's Hacker News.
As you insist though, it's about the energy required to cycle 100,000 miles.