I just had a bowel movement about 15 minutes ago and had a very long (~15 inches), toothpaste-like stool that was half-light brown, half-dark brown and foul smelling.
Could be anything really. Thin stools are caused by how soft they are. If they are very soft, they can come out very thing. The color is not abnormal. Just keep an eye on your BM's the next few days and see if they get back to normal.