Plugin territory functionality; Theme Review Comment

wordpress
themeforest

#1

We are using this code on our theme and reviews saying that this is plugin territory functionality:
https://codex.wordpress.org/Plugin_API/Filter_Reference/user_contactmethods
if( ! function_exists( ‘thimfy_contactmethods’ ) ) {
** function thimfy_contactmethods( $contactmethods ) {**
** $contactmethods[‘facebook’] = ‘Facebook’;**
** $contactmethods[‘twitter’] = ‘Twitter’;**
** $contactmethods[‘googleplus’] = ‘Google Plus’;**
** $contactmethods[‘pinterest’] = ‘Pinterest’;**
** $contactmethods[‘instagram’] = ‘Instagram’;**
** $contactmethods[‘youtube’] = ‘Youtube’;**
** $contactmethods[‘linkedin’] = ‘Linkedin’;**


** return $contactmethods;**
** }**
}
add_filter(‘user_contactmethods’,‘thimfy_contactmethods’,10,1);

Can someone really expain that it can be only add via plugin?