Thanks for the answers. I don't think I would be able to paint it properly, I'm not very handy with this kind of jobs. Even if it's metal, what if I try to clean it with water wet microfiber cloth? Could I damage the metal itself, or is there a risk of it rusting? And what about the back seats, are they protected from the water by the metal? I would like to try at least to clean, because other than the scratches there's some dust and minor imperfections, so if you tell me that water ain't dangerous for the metal itself or the back seats I try to clean it as much as possible.

As above, if you don't feel able to paint it, just leave it as is. Having looked at the picture again, I think there are both scratches and something, possibly paint, on the surface (most noticeably on the bottom right corner).

But I would add that I don't see much point in cleaning it with just water. If you are going to clean it, spray on some general all purpose household cleaner first (but to be clear, that isn't going to remove paint, if that's what it is)

Many years ago I had a hatch with metal backs to the seats. To stop stuff rattling I stuck some carpet to the metal with contact adhesive. That would hide the existing scratches and prevent it happening again.