How to remove unnecessary navigation side bar

Question

I am trying to create a special template page for a group of pages by following Creating a page.tpl.php template for a group of pages (Drupal 7)

I created a page--sales.tpl.php file

<div id="page-wrapper">
  <div id="page">

    <?php if (isset($page['header'])) : ?>
      <?php print render($page['header']); ?>
    <?php endif; ?>
    <?php if ($breadcrumb): ?>
      <div id="breadcrumb"><?php print $breadcrumb; ?></div>
    <?php endif; ?>

    <div id="main-wrapper">
      <div id="main" class="clearfix">
        <?php if (isset($page['content'])): ?>
          <?php print render($page['content']); ?>
        <?php endif; ?>
      </div>
    </div>

    <div id="footer">
      <div class="section">
        <?php if (isset($page['footer'])): ?>
          <?php print render($page['footer']); ?>
        <?php endif; ?>
      </div>
    </div>
  </div>
</div> 

And my content template looks like

<table>
  <tbody>
    <tr>
      <th><h3> <?php print t('Sale Order ID') ?></h3></th>
      <th><h3> <?php print t('Date | Time') ?> </h3></th>
      <th><h3> <?php print t('Download File') ?> </h3></th>
    </tr>
    <?php foreach ($sale_orders as $sale_order): ?>
      <tr>
        <td> <?php print $sale_order['sale_order_id'] ?> </td>
        <td> <?php print $sale_order['sale_order_date'] ?> </td>
        <td> <a href="<?php print $GLOBALS['base_url'] . '/sales/download/' . $sale_order['account_download_id']; ?>">
            <?php print $sale_order['file_name'] ?> </a>
        </td>
      </tr>
    <?php endforeach; ?>
</table>

I assumed that the sidebar won't show, because in page--sales.tpl.php does not render $page['sidebar_first']. But I found that as soon as I render $page['content'], I will get the side bar contents as well.

I think my problem is not understanding how $page['content'] is generated. Do other parts such as breadcrumb and sidebar get "embedded" into $page['content'] before the the page--sales.tpl.php file get processed?

Thanks for your help.