Since the sun has set it must be lit from behind not underneath. So, where does it go? If it were headed straight for the coast why doesn’t it continue on overhead? It is obviously a pic taken after the vehicle has passed and is breaking up.
The sun has set from the POV of the camera, but not from the POV of the contrail which is both miles west toward the sun, but more importantly probably ~30,000 feet higher than the camera. So you see the sun light reflecting off the bottom of the contrail.