The sentence's grammar is vague. The "was" might have been meant to apply to both clauses, so that the driver "was seated" at the time of the crash and then "was moved" during the ensuing mayhem. Or he crawled into the back and died.

The NTSB might have been trying to use neutral language for uncertain events, like how "the position changed" could mean intent or just a force of nature. I don't know what the right interpretation is.