Do you believe “quiet” reserved individuals in any social situation are (whether a mythical idea or not) beta?
Of course they can be alpha, and very often are. You will find that although such individuals are fairly quiet and reserved in a very social setting (e.g. large numbers), when they are 1 to 1 or with people or friends they feel comfortable with or trust, then they can be far more verbal and expressive. When you think that 70% of what people say in a social setting is pure trivia, it makes total sense that anyone thinking on a higher plane (of intellect, perception, whatever) may choose to refrain from ‘joining in’.