Relationship between Fetching a Collection and Parsing its Associated Model

When one calls fetch() on a BackboneJS collection, why and how does parse() in the model also get called? I basically have Board collection and model, and also List collection and model. A List belongs-to a Board. I want to send the List down as JSON data with a Board model (when a "GET" request is called, for instance); however, I do NOT want to send the List down as JSON data when the collection is fetched.

My understanding was that calling fetch on a collection goes through the following steps (never going through the model, let alone the parse() on the model):

index action in controller -> sends JSON/data to Backbone -> the collection receives this data and stores it

I have a collection of boards in that has an associated model:

Board Collection:

TrelloClone.Collections.Boards = Backbone.Collection.extend({
  url: '/api/boards',

  model: TrelloClone.Models.Board
});

TrelloClone.Collections.boards = new TrelloClone.Collections.Boards();

Board Model:

TrelloClone.Models.Board = Backbone.Model.extend({
  urlRoot: '/api/boards',

  lists: function() {
    if(!this._lists) {
        this._lists = new TrelloClone.Collections.Lists([], {board: this});
    }
    return this._lists;
  },

  parse: function(response) {
    console.log("parsing");
    if(response.lists) {
        console.log("inside lists");
        this.lists().set(response.lists);
        delete response.lists;
    }
  }
});

Essentially, for a particular Board model, I send back "lists" with that board:

#in the boards controller
def show
  @board = Board.includes(:members, lists: :cards).find(params[:id])

  if @board.is_member?(current_user)
    render :show
  else
    render json: ["You aren't a member of this board"], status: 403
  end
end

...

#in the JBuilder file...
json.extract! @board, :title

json.lists @board.lists do |list|
    json.extract! list, :title, :ord 

    json.cards list.cards do |card|
        json.extract! card, :title, :done
    end
end

For a Board collection, on the other hand, I do not send back the "list":

def index
  @boards = current_user.boards
  render json: @boards
end

The problem with my above implementation is that when I fetch() the Board collection, the attributes of each Board object are not sent over. But when I comment out the parse() function, everything works fine.

EDIT: I figured out why I wasn't getting data on a collection fetch. I forgot to return response at the end of the parse function. It'd be nice if someone could clarify what exactly are the sequence of steps that occur when a collection is fetched (where the parsing happens in this sequence). Thanks!