I once saw something in Western Kansas which I am certain was an optical illusion or maybe mental blob.
I was driving on a dirt road while on the job. Just as I came over a slight rise, I saw a perfectly formed buck with beautiful antlers, probably a 12 point. He was standing on a small bridge over a dry creek.
I looked down for an instant and looked back. It was a man standing on the bridge! How could I possibly have seen such a perfect image and been completely wrong?
I suspect this is how a lot of ghost stories get started.
Maybe you saw a shape shifter, or as the Indians called them, a skinwalker.