Dull vapour trail at Maryport

Can you see the aeroplane vapour trail in the middle of the picture? It was dark. The plane was on the sunny side of the cloud by this point. I have seen this sort of thing before when a shadow of the vapour trail was projected onto the thin layer of cloud below but there is none such here. I don't think this can be a shadow because I know that shadows can't project onto thin air. So I'm guessing that the vapour trail is reflecting the duller scattered light from the cloud.