Any question answered...

That'll buff out.

How did it happen? I'd file it down before taking the lockring off. As it's the thread that doesnt engage with the lockring when it's fully tightened, it should be fine. Unless the damage extends further than we can see from the photos?

Cheers, just got a bit scared, its my first fixed wheelset, and only had it for about 3 months.
The damage doesn't extend any further so i guess it'll be fine.

Well I only noticed it today, but about a week ago i got back to my bike after i'd locked it outside for work, and when i came back it was clear somone had had a go with some sort of saw as my lock is a bit damaged. Still quite a strange bit of damage for someone trying to cut a lock.