So then when McDonald's introduced breakfast anytime and had ads about having breakfast for lunch and breakfast for dinner they were suggesting fasting all day until you got an egg mcmuffin for lunch or your end of day meal?

I don't disagree with the it started as first meal of the day regardless of time of day, but these days it is more likely to mean morning meal than it is first meal of the day.

There are many ideas conveyed by a single word in English.

You could refer to the concept of breakfast, the meal, and also the common food of breakfast, bacon and eggs, with the same word.

Well it's sort of more of a watertruck really, isn't it?

It does not carry water but it does carry equipment to handle fire.

Firetrucks carry water.

Some do, others carry a large pump and hook up to a fire hydrant for the actual water supply.