From what I've learned Sensei tends to mean someone who has more knowledge on a suject than you or I. That is why the word is used for doctors, politicians, and teachers. The person who has more knowledge, or comes before us, instructs us or helps us in some manner of form.
As for the silent teacher it seems that many of the original students of O'Sensei said that he would teach in this manner. He would show them a movement and then the student would try to copy it. I may be incorrect in this. My sensei also tends to teach this way unless asked. I have had the priviledge of learning some from Kai sensei of the Nippon Budoin Seibukan, Kai sensei is my sensei's sensei. He teads to teach the silent way but does gives "hands on" if needed which I like more. I think you tend to learn more by watching but you don't get a feel for it without some hands on.
Just my opinion.