It could be in the camera (Score 1)

It looks like it could be a static spark in the camera. In the right conditions, the act of advancing the film can generate enough static to cause a spark in the camera and expose the film. It is just a coincidence, that the spark happened at the top of the light pole. There is what looks to me like lightning around the light pole, that is to big to have gone unnoticed by onlookers. The line could be a result of the spark or something unrelated in the processing.