If I'm quiet, I'm usually deep in thought.
Quiet with a frown...steaming mad....deep in thought about revenge.
When I'm around people I know, I'm pretty talkative. If I'm surrounded by strangers, I'm very quiet, and even rather shy.
I'm a thinker and am often quiet. So I guess that is what it means most of the time. I was always a bit shy and quiet but have forced myself to get past that. It's still sometimes painful to come out of my shell but I do it! People have a hard time believing this about me.