1956 Nickel - Can Anyone Please Explain What Happened Here?

It looks like someone has done a poor job of replating your nickel.
An Original 56 nickel is made from a copper nickel alloy so there
is no way that could happen when the coin was struck.
It is considered a damaged coin now.

Well, for starters, it's a proof nickel. The steps pretty much guarantee that. Proofs can look strange when photographed. It's not unheard of to have some warping in a late die state, but that grainy texture implies plating, as Jimmy already said. A proof nickel could still be that shiny, though, especially if someone used a polishing agent on the surface.

What I find odd is that plating should have messed with the narrow grooves in the steps, but they seem ok. Is it possible that the graininess is camera artifacts?

A weight to two decimal places would probably help a lot. Proof nickels are generally right on the nose at around 5.00g, and if it's significantly more than that, plating is the foregone conclusion.

Yes, an accurate weight might reveal more.

I agree, a heavy coat of lacquer blankets this Jefferson nickel...

with above comments.

Hopefully you can find it again and get it weighed.