I'm pretty sure that John covered, in his article, the semantics of the word "idea". He drew the line between an idea and your notion of "brainfart" with a 10 page business plan. I guess he was trying to make the point that if the idea is truly going to revolutionise whatever, then at least a 10 page business plan would not be a big ask, and would show that it is more than an in-shower brainfart.