Truck's fault. All he had to do was to be patient, going around the slower vehicle in front. I don't expect truckers to be patient though, they treat everyone else as inferior on the road. I guess men in control of powerful machines usually do that... if they are dumb, which most of them, such men, are. How many times have you been stuck behind two semis going next to each other discussing their glorious life over the radio? Trucker is not a role model of a good/patient driver.
AP's "fault". Bridge. Shadow. White truck. NN failed to see, simple as that. Usually AP brakes even if the car in front is over the line just a bit, unless it fails to recognize that car. You could imagine that getting NN to learn this object is pretty hard, because it's RARE and DYNAMIC data with shadow moving over time during the day. I would imagine FSD rewrite (currently limited beta release, not public) will fix this all together as it will now track objects over time and not per every frame like in current version. It should reduce the probability of these events.
Driver's "fault". Don't trust the AP. When I drive on the highway I use AP all the time. Just AP, not NoAP. BUT! I always, always, always watch out for known bugs like bridges, trucks and trailers, construction zones, weird looking vehicles, poor lane markings, UFOs (whatever derbies that fly into the car), when passing very active junctions, weather conditions, etc, etc. It is an assist, not FSD. I only relax using AP when in between heavy traffic zones, in between cities, etc. Otherwise I watch like I normally would, while it's keeping the lane. I might let off when I see ahead on the straight line and traffic is calm, weather is good and I'm NOT in the left lane. Also AP does not read blinkers yet.
If driver failed to see the blinker and make a safe bet from inexperience it's still truck's fault. Insurance charges younger drivers or drivers with bad record for exactly that reason. Some people just fail to learn or use common sense too.