But it may have been so broad and vague as to challenge his very right to challenge engineers by whatever definition.
I don't think it was broad and vague at all. It was probably very specific -- like the laws and regulations in my own state. Simply using the word "engineer" to describe your professional capabilities in the context of a matter that is within the professional purview of a licensed engineer is considered a violation of these regulations in my state if you are not licensed in this state.