this sort of nomenclature gap happens a lot with food. the people that are preparing the food categorize it differently than those that are eating it because of the slightly different areas of focus. chefs will often refer to eggs as “dairy” items because traditionally a dairy farm is where one would purchase eggs, but the term is commonly used by medical personnel and their patients for describing cow milk and all other derivative products that are eventually made with cow milk in it. so a person who is lactose intolerant may say “i cant have dairy” and a ‘classically’ (see: french) trained chef will automatically assume they cant have mayonnaise or anything else with egg in it. source: me, a waiter in california for 14 years.