Due to the location, this was probably caused by the machine stitching the welt rubbing the upper. It happens quite a bit. If it isn't very noticeable when your wearing it, I wouldn't worry about it as it's on the medial side and small scuffs will probably accumulate in that area over time. Can also try to brush it out a little bit if you haven't.
8/20/15 at 1:43am