function add_member_field( $meta_fields ) {

    $meta_fields['member_bought'] = array( 'label' => 'Member Bought', 'group' => 'woocommerce' );

    return $meta_fields;

}

add_filter( 'wpf_meta_fields', 'add_member_field' );

function get_member_data( $order_data, $order ) {

    foreach ( $order->get_items() as $item ) {

        $product_id = $item->get_product_id();

        $product_terms = get_the_terms( $product_id, 'product_cat' );

        foreach ( $product_terms as $term ) {

            if ( $term->slug == 'membership' ) {

                $order_data['member_bought'] = 'YES';

                break 2;

            }

        }

    }

    return $order_data;

}

add_filter( 'wpf_woocommerce_customer_data', 'get_member_data', 10, 2 );