The way the trail is dissipating in the lower part of the image is the key. Rocket trails go from lower atmosphere to upper atmosphere and don't disperse in the same way at different points because wind speeds, directions, shear, etc all vary with altitude.
The lower part of that trail is all smearing off to the left in a uniform way which indicates it's all at the same altitude. No rocket will fly to an altitude, stay there for awhile, then climb again. That's an inefficient launch profile plus it puts stress on the rocket. Oh, and rockets move REALLY fast.
It's an airplane.
I once saw a contrail like that form here. It was also at sunset, off to the west of here, and it just started at altitude slowly heading north. When it first started it looked very odd because it was so short so it almost looked like the contrail was the object itself. After about 5 minutes though it was long enough, and you could watch it getting longer to the north at a nice slow rate, that it was obviously a distant airplane.