How to access jQuery plugin added through libraries API
Found the problem - this library comes with two separate files, one that is a straightup javascript library and another in jquery that registers the file as a plugin (smallworld.jquery.js)

  $.extend($.fn, {
    smallworld: function (options) {
      var opts = $.extend({}, $.fn.smallworld.defaults, options);
      return this.each(function () {

      $(this).data('smallworld', new Smallworld(this, opts));
      return this;
    });


To get this to work, I had to take the whole 'register' script and add it to the jquery file script I created for the module, ex:

(function ($) {

  Drupal.behaviors.smallworld = {
    attach: function (context, settings) { ...