It was a model rocket engine that was ignited by the film crew just before impact to ensure that any spilled fuel caught fire. Which it did because they overfil

It was a model rocket engine that was ignited by the film crew just before impact to ensure that any spilled fuel caught fire. Which it did because they overfilled the tank and used the wrong gas cap for that model year truck. Apology starts around 1:40 https://www.youtube.com/watch?v=ADOwKSal17I https://www.youtube.com/watch?v=ADOwKSal17I