Had a customer send back this AR10 bolt

Ok I will ask the question. Why did he send it back? I know that sounds stupid but he wouldn't have used a dewalt 7 inch grinder on it without a reason. At least I would hope not. I am not saying there is (or was) anything wrong with it i just am sure there is a funny as hell story that would add to the picture.
I imagine that the gun was not cycling fully and the bolt was picking up a round in the middle of the case and jaming. Pretty sure we have all seen that. Usually weak ammo, not enough gas or to heavy buffer/spring.
just wondering what the hell he was trying to accomplish.
 
Serious question for you AR experts. How much would this amount of damage actually effect the functionality/safety of the rifle?

Personally, I don't think I'd ever even consider grinding the locking lugs on any of my rifles, but it's interesting to see that not everyone is as reticent as myself. Maybe he was going to do some kind of 'Mythbusters'-like test, where he ground more and more of the lugs offf until he ended up with a load of scrap metal embedded in his head?