LOL!

Looks like a piece of art in the Andy Warhol Museum... titled "Urine on Copper".

It's acid treated metal. Chemetal makes some real metal high pressure laminates with similar, but I think better-looking finishes.

Here is a link that might be useful: Chemetal

looks like stained concrete. i doubt that's what it is, but i've seen stained concrete floors that look like this in restaurants.

It says in the lower left corner: "rusted metal" Or, do you think someone just titled it that?

It definitely looks just like rusted sheet metal (steel)