I'm not really sure what kind of response you're looking for here, but I'll do my best.

It was dark. You were probably tired. You were looking for things to happen.

In all likelihood, nothing happened that can't be explained away. Black figure behind the trees? Well, it could have been an actual figure. Or it could have been anything; a mannequin, a tree, a trick of the light. You can 'see' all sorts of things in the dark, especially when you're creeped out already. And the things on the windscreen? They could have been there already. One of your friends could have done it in the panic. Or they could just be dust trails or from washing; that can happen too.

If I were you, I wouldn't sweat it :)

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Down is the other direction.