it's hard to know if something's wrong just from looking. if you can drag your finger nail across the surface and it doesn't catch on anything, then it's really just cosmetic.
Yes, I agree with you.
I ran my finger nail across the surface and it does appear to be some sort of deposit.
The Tungsten Carbide coating should resist lots of materials with the exception of diamonds or similarly very hard minerals. I can't imagine that salt or road grit would damage the coating.
Any rock or stone debris that gets caught between pad and rotor will damage the coating like your rotor clearly shows.
Your pads are damaged too btw.
Is that the front rotor?
In my country that car wouldn't pass any APK (annual safety inspection).