Hello , actually I found my statement here, from the great French typographer Jean-Pierre Lacroux, who cites the source I gave you (paragraph #3): 
For your question, Jean-Pierre Lacroux defines the em as it is defined in the Wikipedia article so the answer to your question (2) is clearly no. Now for your question (1) I cannot answer based on what Jean-Pierre Lacroux says and I don't have access to his source (which is one of the most reliable source for French typography).