Well if u have 100 of orderid='$line[orderid]' (ex. orderid=10) and like 50 itemstatus = 'SHIPPED', this select is colecting u all the 50 orderid that have itemstatus = 'SHIPPED'.
If u wnat to check only one item that have itemstatus SHIPPED, this means u know the item id and we will call it '$id', then u have to tell to mysql to show u the itemid='$id' that have itemstatus = 'SHIPPED', if is not showing u the item then that item is not SHIPPED.