The silence spoken of here is that of beyond the mind, and therefore of beyond control or lack of control of the mind etc. The silence of Self, or awareness only.
“What did Dakshinamurti, the Supreme Guru do? He remained simply silent and the doubts of the disciples were dispelled: they lost their individualities. This is Jnana, and not all the verbiage usually associated with it.
“Silence is most potent in its effects. The Shastras, however voluminous and emphatic they may be, fall far short in their effect.
The Guru is quiet and peace pervades all. His silence is vaster and more effective than all the Shastras put together. These questions arise because of the feeling (among some) that, having been here for so long, heard so much, exerted so hard, one has not gained anything. The work proceeding within is not apparent, though the Guru is always within you.”