looks like just a pin in there, pretty shure it's something relative to the breakage of the arm or something for warranty like the sunflower paper in cellphone. Not shure

 could it be from the hollowtech process ??

 probably, i talked to one of my friends that is secialized in materials he said it's probably due to fatigue but maybe there was an air bubble in the metal somewhere and it caused to fail at that point. there is many theories but we will probably never know

 defo a bullet