Piklist uses a 12 column grid. So each row of fields should equal 12. Try this:

piklist( 'field', array(
  'type' => 'group',
  'field' => 'home_news',
  'label' => 'Featured News',
  'description' => 'Information for the home page news feature.',
  'template' => 'field',
  'fields' => array(
    array(
      'type' => 'text',
      'field' => 'section_title',
      'columns' => 8, // First row: 8 columns
      'label' => 'News Section Title',
      'value' => "What's New",
    ),
    array(
      'type' => 'number',
      'field' => 'section_quantity',
      'label' => 'Number of Posts',
      'description' => 'How many recent posts should we display?',
      'columns' => 4, // First row: 4 columns. Row will end here because 12 columns have been reached.
      'value' => 2,
      'validate' => array(
        array(
          'type' => 'range',
          'options' => array(
            'min' => 1,
            'max' => 4,
          ),
        ),
      ),
    ),
    array(
      'type' => 'text',
      'field' => 'section_link_text',
      'label' => 'Text for Link to News Page',
      'value' => 'View All News',
      'columns' => 12, // Second row starts here
      'validate' => array(
        array(
          'type' => 'safe_text',
        ),
      ),
    ),
  ),
));