I tested your code in a custom module and it working for me. I have two differents outputs. Test it and let me know if it working for you.
function mymodule_menu() {
$items['graph'] = array(
'title' => t('Sample Graphs'),
'page callback' => 'graph_content',
'type' => MENU_CALLBACK,
'access arguments' => array('access content'),
);
$items['graph/line_graph'] = array(
'title' => t('Line Graph'),
'page callback' => 'line_graph_content',
'type' => MENU_CALLBACK,
'access arguments' => array('access_content'),
);
return $items;
}
function graph_content(){
return 'hello '. __FUNCTION__;
}
function line_graph_content(){
return 'hello '. __FUNCTION__;
}