If you enlarge the photo, just up and right of the top of the nearest street light there is some faint wispy cloud. The picture hasn't quite conveyed what I saw but there seemed to be thin delicate lines of cloud like strings. This is a minimal form of the mackerel sky I've posted about before. It isn't lenticular cloud but I know that lenticular cloud is caused by stationary wave patterns where vapour condenses into the antinodes. This is such a regular periodic pattern with condensed vapour between clear gaps that I'm wondering if it might be some kind of stationary wave.
