Hairline scratches that can only be seen under indoor lighting are most likely scratches in the oleophobic coating, which is pretty normal.
Hairline scratches on the body are VERY common if you're caseless because aluminum is such a soft metal that attracts scratches very easily.
Anodised aluminium is very hard and oleophobic coatings are as well.
Actually of all my smartphones, i don't recall seeing a scratched coating on either the case or the screen coating outside of a drop or chip
It looks like I may have similar scratches on my 6+ so I would also like to know the answer to this question, and otherwise what I might be able to do to repair them. Thanks!
I'm not trying to be a dick so please don't take this the wrong way. What would make you think that scratches would get smaller or heal themselves in other words?