I'm unsure that it was actually strategy used by Vito's mom to save her son. In the book, he "awoke" his intelligence, by apply what his intellect to the Fanucci situation. It was even stated that before then he never used his mind in this way. I do think he was a bit slow, quiet and seemingly dumb-witted. He was slow to react in the movie and very introverted, the later point, especially in turn of the century Sicily could be construed as dumb-witted.