Since you are asking, it seems that it bothers you, so contact the seller.
In the photo doesn't look much, but if the surface doesn't have the same gloss/granularity like it would be acetone damage, then chances are, in time, that area will accumulate dust and fingerprints grease hard or impossible to clean, and make it very visible and dirty like a floor scratch.
Later edit:
Just checked and my DS1054Z doesn't have that kind of surface finish damage.