Good theory, but it's not universally the case. I know plenty of people who are all of those things, yet very quiet.
One reason I see is, that they feel they are happy within themselves and do not feel they need to share with the world how they feel. They are positive about themselves and their lives, so they aren't to "show this to the world."
But what I'm getting at is all loud, outgoing and friendly people exhibit those characteristics. Not the other way around.