My best guesses:

1. It was indeed hemmed and left that way for enough time for the new edge to get some wear that appears as the roughed up line after the hem was released---kind of a hem wear scar, if you would
2. Maybe is is simply a bad turned in selvedge instead of a proper kilting selvedge---one of my kilts has a turned in selvedge which is visible as a similar line in limilar location but less so than your example