The mystery is, why would anyone be digging for veteran graves to auction off the craniums?
Yes that is kind of strange.
I’m pretty sure digging in a federally protected place like Gettysburg is against the law, and selling of human remains is of course illegal.
I have a feeling there is a big "rest of the story" here that hasn't been made public yet. Somebody probably defrauded somebody. And even if the original story were true why wouldn't veterans organizations and/or the Army insist that this skull be treated as human remains and not a souvenir?