A lot of those bent wire pieces look like staples from a pneumatic stapler, like the one’s used for construction. Or they could be wire used to generate shrapnel from some sort of improvised mine. A landmine constructed from a wooden box and wrapped in fence wire could do some serious damage.
I tried to think of a wire source too. Perhaps something to wrap something like a box or casket. In your box scenario, it would seem the wire would blow in all directions if it was a wrapping. If the wire had been previously cut, I could see it blowing out, but it seems like that would have been in all directions too.
Some of those long pieces, couldn’t have entered the skin and remained inside. They could have been picked out of the resulting wound with little problem. They wouldn’t imbed at length submerged so as to be out of reach of forceps or another tool.