It seems like everyone is mentioning this, and I don't understand how we know that the Engineer friend wasn't the one driving, with the Doctor owner sitting in the back - possibly to take a video for his friend, or to better observe and coach him....The whole jumping in the back seat explanation just hasn’t sat well (and why would he then buckle in in the few seconds he had before reaching the trees?)...
This version makes a lot more sense to me, especially the point that someone much less familiar with the car would be much more likely to be startled by the unexpectedly strong acceleration and lose control.
In this scenario, no one climbs over the seat, which is considered difficult though not impossible. The Engineer, after crashing the unfamiliar car, cannot get out on his side and moves to the passenger seat but cannot exit that side either. Soon, both succumb to the toxic battery-fire smoke and are left in the positions found by the firefighters.