Hot Rods HEI wear-pitting mystery

Or could it be the hole had those flaws all the way around (casting?) and the broach went deep enough in the corners to get through it?

 

Before a hole is broached it is roughed out by drilling a slightly undersized hole. Sometimes a chip welds itself on to one of the drill flutes and gouged up the side walls a bit. If you look carefully you can see the marks are circular in nature. No doubt in my mind what is from.