Looks like the previous owner may have rested the slide on the frame when field stripping. The slide sharp edges made those lines.
As it is Stainless you could use 1500 grit sandpaper to buff them out by hand .
Yes I think that is typical marks you can find on many PP pistols because someone wasn't holding the slide all the way rearward when installing or removing it. On the other hand....it seems some of these pistols had extremely tight tolerances with regard to retracting the slide far enough due to the recoil spring. There is a nearby thread on the very problem. If you drop by a drug store or grocery...you can find some very nice packages of emery sanding sticks in the fingernail stuff area and from very fine to medium that give you excellent control of cut and direction. Be sure to match the same direction of the existing buffing and don't remove too much material. 1917