Not only Buddhists, but Taoists in Taiwan don’t eat onion or garlic. Vegetables from the onion family can be considered “hollow vegetables”, and they are not considered to be vegetarian. They are quite sensitive about this; if the knife was used to cut onions it needs to be washed before making vegetarian food. Also many kinds of cheese are not vegetarian because almost every kind of cheese contains enzymes taken from the stomach of a baby cow.