Oh, I remember seeing this on reddit.
According to the driver of the truck, he was hauling a trailer loaded with two cars.
The reason the truck drifted off to the left to hit the silver car, is because the truck jumped the hood of the red car, which caused the truck's suspension to break, and it snapped his steering rod, which means he had no steering.
The truck driver came out fine, with just some bruising from his seatbelt. The two other drivers were pretty badly injured, one with broken ribs, and one with a head injury, I believe.
Insurance company and cops both agree that it's red car's fault. I don't know more, but bet their insurance just went way up.