Do still water run deep true for everyone?

Do you realise that when people are quite others will say that he /she are still water run deep...but i found out that this didnt came true to someone that are usually quite ...

Here are some reason i get ;

1)they have no topic to talk to others

2)they are afraid to chat with other  (= lack of confident)

3)they dont like to talk to others when it is not giving any benefit on their job or studies ( which they call as NONSENSE)

4)they like to be alone

5)they want to be  mystery (so that others will find them intersting)

6)always in a moody situation( which is very unhealthy and may causes autism)

*this is some of the reason i know yet i think there's still alots of reason can be found .

ps; people who lack of confident always speak very softly..

  This prove that not all those quite people are still water run deep..there's only few of them have this characteristic