If an historical event is presented in a secondary work with primary evidence, then that evidence is primary within the secondary work. If Becke is quoting Napoleon, then that portion of Becke's work is primary, and hence contemporary. There are many secondary works (not Becke's in this case) which are full of primary source material, so much so that they can be classed as a primary work even though they have been authored/edited by a later author. Saski is an excellent example, as is Girod de l'Ain in his work Grands Artilleurs. Both of those books are loaded with primary source material which outweighs anything the listed author says in them.