You're right, it does seem like the truck likely would've been forcing the car behind to brake. And that's bad behavior. I wonder what speed the truck was act

You're right, it does seem like the truck likely would've been forcing the car behind to brake. And that's bad behavior. I wonder what speed the truck was actually going at. Letting off the accelerator probably would've only slowed it down to 60mph. On the other hand the Tesla probably shouldn't have been going that fast when the speeds of cars in both adjacent lanes are going that much slower. I'd expect a human driver would typically feel more wary in such a situation, wary for that exact situation of a truck changing lanes.