That's an amazing factoid. "NS" standing for NeXTSTEP would then be a popular misconception, then. It also introduces an interesting hypothetical of what if Sun ended up adopting OpenStep, if Java was not developed in time or fell through or whatever.
The OpenStep spec was a collaboration between NeXT and Sun. OpenStep was available as a full OS (for 68k NeXT hardware and 486 beige PCs) as well as running on top of Solaris (SPARC), HPUX, and Windows NT. Sun went with Java instead but Microsoft has a WinObjC project. Go Figure. Until 10.7 or so, OS X still included Windows NT theme graphics [1].
NeXTStep 3.0 used the NS namespace; 2.0 and earlier was NX.