‘manage_users_custom_column’ is a filter, but ‘manage_posts_custom_column’ is an action. Why?

‘manage_users_custom_column’ is a filter, but ‘manage_posts_custom_column’ is an action. Why?

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)