Because the single choices value is not a string but an array of values itself.
http://www.advancedcustomfields.com/resources/get_field_object/
So you’d need something like:
<div>
<?php $field = get_field_object('engineering');
$value = $field['value'];
$choices = $field['choices'];
if( $value ):
foreach( $value as $v ):
echo $choices[$v]['label'];
endforeach;
echo '.';
endif;
?>
</div>
