It’s not uncommon for waitstaff to lack knowledge of the menu.
When we visit a restaurant, we usually assume that the server or the waiter is well aware of the menu. Well perhaps, this is not always the case and the waiter may have some basic knowledge of the menu. But the chances of them knowing each and every ingredient are very rare.
When we inquire about some particular dish and the workers don’t have information: they either recommend you the dishes they know the ingredients of or either they make a run to the kitchen and enquire the chef. So we should no take offense if the worker isn’t all-knowing about the menu and we shouldn’t let it affect the tips at all!