You also could have hit the "harmonic" of the double-line bokeh that the lens makes. That is, if you take a photo of a straight edged object that contrasts from its surroundings and focus on it, you'll get the edges in focus, of course. Once you begin to de-focus the object, it will become fuzzier but the edges tend to have a bit more density in them than the center. Not quite doughnut bokeh but close. In this case, I think the roof gable may have had another parallel line nearby and as you move further away, you may reach a point where the two de-focused lines hit an overlapping area as a function of the edge of the bokeh of both lines to create the thin, sharp pencil line we see here. A kind of moire frequency but without the grid.
Maybe I'm reaching, but I've seen it before in a few of my shots with digital cameras.
Then again, it could just be in-camera jpg processing if that's what was captured instead of a raw.
Phil Forrest