3col stacked layout: bottom only 4 columns?

From docroot/sites/themes/zurb_foundation/layouts/foundation_3col_stacked/foundation_3col_stacked.tpl.php

<?php if ($content['bottom']): ?>
  <div class="row">
    <div class="large-4 columns">
   <?php print $content['bottom']; ?>
    </div>
  </div>
<?php endif ?>

Why is this using 4 columns? Should it be 12?