So the rear bumper had been hit or something, it was scuffed deep into the paint, it was through the basecoat so it needed respray. I asked them if they could fix it and all and they said yeah (was added job to insurance job). Now, when the car is really clean or really dirty it's perfect, but as soon as you get maybe a little bit of dirt and dust it starts to look like this. The smudges are my finger swipes to show.

Now my question is, does this mean it wasn't blended correctly, of the sanding wasn't feathered properly or can anyone identify what may be wrong, or if this is expected when there is dust in a blend?
Thanks! By the way guys, I do a few posts but everytime I learn stuff and it helps me out so I thank you very much!