Soot on Dinghy

So update...I wasn't paying attention to the issue before a friend of a friend who was a Cummins mechanic, told me there really shouldn't be noticeable dirt/soot. I have attached pictures of the car, the tailpipe and the mud flap that looks like it too has soot on it. I had noticed this previously, but chalked it up to running the engine at a campground where the mud flap was laying on the ground, or close to it, it wasn't hanging as much as laying on the ground due to leveling. The tailpipe looks pretty clean. Even wiping it with my finger doesn't show much.
OOps having an issue with loading pictures. Will post separately.