I believe the first quote, "Never kill a man who says nothing," could relate to the fact that wise men listen. Thus never kill a wise man. Wise men are needed for their wisdom.
In the quote, "There is nothing to fear from someone who shouts," it could be said that fools talk loud and say nothing. Foolish people do a lot of talking, even shouting, but in actuality, they say very little. Fools do a lot of taliking that amounts to little action.
In the quote that states, "There is no story that is not true," it could be said that every story has an element of truth. Although it can be twisted around, there is always an element of truth. As I heard someone say, there are three sides to every story--his, hers, and the truth. Although there are three sides, all of them contain an element of truth.