I've been to Antietam and if I remember correctly there are a lot of soldiers buried there from both sides. How to account for the find? A body was inadvertently left unburied in the rush to clean up the battlefield (a tour guide mentioned that soldiers were buried so fast some of them are thought to have been still alive but unconscious)? If that was the case, why haven't these fragments been discovered long ago? A ground hog dug up some of the remains? Can a ground hog dig six feet down? Were some of the hastily dug graves shallower? Remnants left by grave robbers? Paranormal activity? These are some of the possibilities that occur to me.

It is certainly curious. If anyone has further information I hope they post here. My husband and I are both interested in the Civil War, so I'll be looking for more news on this.

I was reading more into the second article and they said what you said. People were intended to be buried and were not. Or it was a shallow grave.
And this person was positioned just so that nobody ever saw him. Apparently it is a corn field and crops have been planted around him all that time.

Kind of nice to see someone finally found though.