Why is this PHP array not the same?

PHP Snippet 1:

array( 'items[0][type]' => 'screenprint')

PHP Snippet 2:

$data = array('items' => array(0 => array('type' => 'screenprint')));

PHP Snippet 3:

$data = [
    'items' => [['type' => 'screenprint']]
];
echo $data['items'][0]['type'];