The crash took place on Taiwan's National Highway 1 and there's video of the wreck, and you can see the Tesla drives right into the truck, with only what looks like a solitary attempt at braking just before impact.
For any human driver paying even the slightest bit of attention, this accident is almost an impossibility, assuming the driver had functional brakes and was not Stevie Wonder.
Tesla's autopilot system primarily uses cameras for its system, and previous wrecks have suggested that situations like this, a light-colored large immobile object on the road on a bright day can be hard for the system to distinguish.
In general, immobile objects are challenging for emergency automatic braking systems and autonomous systems, as if you use radar emitters to trigger braking for immobile objects, cars tend to have far too many false positives and unintended stops than is safe or desirable.
The Fourth Highway Police Brigade said that driving Tesla was a 53-year-old man named Huang, who claimed to have turned on the vehicle assist system at the time. It was thought that the vehicle would detect an obstacle and slow down or stop, but the car still moved at a fixed speed, so when the brakes were to be applied at the last moment, it would be too late to cause a disaster.
Nobody was seriously hurt in the accident.