Quitennes doesn't mean inability to speak or be vocal it sometimes mean being prudent with words, being discrete and being wise.
We are advised to be quick to hear and slow to speak. A person who is able to bridle his or her tongue has saved himself from a lot of troubles and proven to be wise.
Also, based on temperament categorization, some people can be considered as characteristically quiet. There are people who will can be extremely quiet, tho people consider them to boring, but it's just their nature and they are able to stay away from so many troubles.
I would say I behave that way too. When I get into a new environment, I remain quiet just to observe and learn, so i can flow with people smoothly and this has helped me alot.
