Hi!
"package.nw" file contains the game (in mac app.nw i think), the other files just the NW.js browser
If you can update "package.nw" file you can update the game.
If you want update the NW.js itself you need update all other files.
You can create an updater with NW.js (Ajax + NWjs plugin). Game download the updater in a temp folder and updater update the game