Check the database for a postmeta field

You don’t need to set a new WP_Query since you are looping through the data of the octopus. I would do the following in your case:

Create a function that checks if there is a post with an octopus_id given

function post_with_octopus_id_exists( $octopus_id ){

    //If for some reason the $octopus_id given is empty return false
    if( empty( $octopus_id ) ){
        return false;
    }

    //Do a meta query to fetch posts with the given $octopus_id
    $args = array(
       'post_type'      => 'employee',
       'post_status'    => 'any'
       'meta_query'     => array(
            'relation'  => AND,
            array(
                'key'       => '_octopus_id',
                'compare'   => 'EXISTS'
            ),
            array(
               'key'        => '_octopus_id',
               'value'      => $octopus_id,
               'compare'    => '=',
           )
       )
    );

    $the_query = new WP_Query( $args ); 

    //if there are posts with the given $octopus_id return true otherwise return false
    return ( $the_query->have_posts() ? true : false ); 

}

Then inside your loop you can call the function as following:

foreach ( $records->data as $record ) {

    if( ! post_with_octopus_id_exists( $record->id ) ){
        echo "Hello";
    }

}

Important: Make sure that the meta_key stored for each post is named as “_octopus_id”