The coin was apparently in a fire which brought the Copper in the composition to the surface of the coin. With the exception of the War Nickels, the Jefferson Nickels are 75% Copper and 25% Nickel.
Looks like a digger to me. Meaning it was once in the dirt and found after many years by a detectorist and returned to circulation. I find a bunch of them and they look very similar.
Or, it could just be a very dirty nickel.