Nos?????

I'm bidding on a water neck elbow on eBay that was listed as

1961 PLYMOUTH VALIANT 1962 1963 VALIANT PLYMOUTH DODGE
NOS WATER NECK ELBOW PART # 2121 524


I asked the guy if that was aluminum or cast and he says it is aluminum. If it is aluminum, wouldn't that make it an aftermarket replacement piece and not NOS?