It took a lot of force to warp the metal into its current shape. Could this piece be from a section of the NC that was twisted when the stern broke off?
Maybe, but it looks too thin to be hull plating.
half inch hull plating was quite heavy at the time. the thickest readily available plating in 1911 was 1" according to the many sources that research the Titanic also built in that year. So much so that things like reinforcements were made from two sheets of 1" plate riveted together instead of thicker material. The 882', 46,000 ton titanic used one inch plate. Given the Norwich City was 397' and 8730 tons it would use significantly thinner hull plating.
I have also read that many manufacturers would use iron rivets in the steel plates still because they had a hard time forming the steel rivets correctly. the outer section of the hull plate should have a countersink to the hole. the outer plating would be formed and attached differently than other structures to maintain strength without sacrificing hydrodynamic efficiency or ease of building.
however these pieces landed where they did, my armchair theory would be it was hull plating torn off during the initial impact with the reef