Shyness is a matter of confidence. Is the person confident when they do speak? If so, they are introverted. Are they awkward and inconfident when they talk? They may just be shy (but introverts can be shy, so you don't know if it's a shy extravert or a shy introvert).
So, as Pheonix said, it has little to do with extraversion/introversion.
__________________
|