To be honest, it looked more like a brush stroke from a giant’s paint brush than any particular sort of cloud. You can get a similar effect if you wipe the paint off a paint brush on to a piece of paper. Meanwhile, what kind of cloud is it really? Does it count as a low-level or a medium level cloud?
We looked up “The Met Office Pocket Cloud Book” as well as “The Cloud Book” and a flow chart type of key called “The cloud name trail”. None of them gave us a definitive answer but we narrowed it down to two: some kind of altostratus (flat medium height cloud) or stratocumulus lenticularis (a flattish low-level cloud). Or put another way: a not very high ovalish sort of cloud. See what you think: