They didn't deploy the code. That's not how this exploit works. They _downloaded_ the code to their machine. And npm's behavior is to implicitly run arbitrary code as part of the download - including, in this case, a script to harvest credentials and propagate the worm. That part has everything to do with npm behavior and nothing to do with how much anybody reviewed 3P deps. For all we know they downloaded the new version of the affected package to review it!