The oyster shell pattern in the center makes me think somebody drug a welding rod on it. But I don't know how it would not discolor the coin. If someone has a stick welder they might want to try to re-create this.
Looks like it was done with a Tig type welding machine. It uses a gas to cover the arc point and is very precise in a trained hand. Yes to heat damage.
look t Lincolns head, it could be an error, I guess. its faded. Don't chance it though look at the experts opinions.
It could have been dipped or cleaned to bring it back to one color if it even needed to be. Tig weld is so precise the heat transfer would have been minimal. And I think it has been a few years since it was damage. https://en.wikipedia.org/wiki/Gas_tungsten_arc_welding
I don't know what caused this after it left the Mint, but I have to say that it is, by far, the strangest looking PMD I have ever seen. Chris
What does the seller claim it is? It looks to me like it was soldered into a mount, and later removed.
If it were struck like that, there would be weak details on the other side as that blob looks raised. Even minor lamination flaps have areas of weak details on the other side. I just don't think it is genuine.