That it's a symbol in a Cocoa framework :)
NS hasn't had anything to do with NeXTSTEP since, well, NeXTSTEP. The author's wording makes it sound like this is some crazy remnant of forgotten 30-year-old code poking through, but it's really not. It's Swift (most likely) string concatenation being passed a view instance instead of a string by mistake.
That’s kind of a weird take. It’s perfectly reasonable that Apple has not attempted to yank all the “NS” references out, but they are absolutely a holdover from NeXTSTEP. That NeXTSTEP no longer exists does not change that.
What would you say the letters NS stand for? Perhaps "Not Standforanything"?