Defective equipment as in a fire extinguisher malfunctioning. Would have indicated a proper pre patrol check of his vehicle was not preformed. These failures are usually by inexperienced officers or officers who have become complacent in their duties.
Since we do not know what the posted speed limited was on the highway this could have been simply a less than 10 MPH driving over the posted traffic stop. If the posted was say 65 then this would have constituted a careless and reckless stop. In either case administering a pullover in high dry grass is never recommended a more prudent activity would be to PA the driver explaining for him to continue on until a safe pullover location could be established. Obviously if it were suspected the driver may be inebriated, under the influence or having a medical condition getting them to stop at first opportunity is best.
In the video it appeared that once the patrolman reversed his vehicle away from the fire the first time a second fire was started from under his vehicle. He was screwed at that point no matter what he could have done short of reversing onto the road way surface and stopping in a lane of traffic the number 1 no-no to be avoided at all reasonable costs. Even had he done so the fire was still going to spread While it was contained in a very small area he probably could have kicked it out and only gotten his shoes and uniform a little soiled, but his hot exhaust was still going to ignite secondary fires anywhere he could have parked in the dry grass.