Dropdown filter in custom posts

When using this hook, your function receives two parameters, onde of them is the slug of the current post_type;

<?php
function my_post_type_filter($post_type) {

  $post_slug = $post_type; 

  if( $post_slug == 'the_post_type_slug') {
    // Do something
  }
}


add_action( 'restrict_manage_posts', 'my_post_type_filter' );

?>

To learn more about this hook check the Docs.