While this may sound like a pretty open-and-shut case, it highlights how some Tesla owners might not fully understand how to properly wield Autopilot's power. Autopilot's name makes it sound like it's a Level 5 autonomous driving technology, but it's really more of a driver assist tech in its current form.
The previous Tesla vehicle incidents that US safety regulators investigated also involved drivers whose hands were off the wheel or weren't paying attention to the road. Tesla even issued a statement insisting that the Model X accident in Mountain View, which killed Apple engineer Walter Huang, wouldn't have happened if he was looking at what's in front of him. (His family said the vehicle veered towards the barrier he crashed into before the fatal accident itself, though, and believes Tesla doubled down on putting the blame on him in order to distract from their concerns regarding Autopilot.)
Tesla has long been the target of criticism for not equipping its vehicles with extra safety measures to ensure drivers keep their hands on the wheel -- something the company says people must do at all times while on Autopilot. A recent Wall Street Journal report said the automaker nixed plans to put eye-tracking and steering wheel sensors in its cars due to concerns over cost. Those sensors would be able to warn users if they take their eyes off the road or if their hands wander elsewhere. Tesla chief Elon Musk, however, refuted the accusation and said that the company chose not to incorporate eye tracking, because it was ineffective.
As for this particular incident, Musk expressed dismay that a "Tesla crash resulting in a broken ankle is front page news" while the "~40,000 people who died in US auto accidents alone in past year get almost no coverage." He said another car hitting a fire truck at 60 mph would've resulted in severe injury or death.