From what I can tell[0], left-pad was released under the "Do what the fuck you want public license"[1], so I suppose NPM can do whatever the fuck they want, including redistribution.

[0] https://www.npmjs.com/package/left-pad (although I suppose its possible the library was added after the package was re-added -- I don't see a license on the GitHub page)

[1] http://www.wtfpl.net/