Lol, I'm glad I'm not the only one who was confused by this.
I guess everyone has their own definition of shy. To me, shyness is what others in this thread are saying: social anxiety in its mildest form. Everyone gets shy about something, whether it's approaching someone of the opposite sex or performing in front of an audience. Shyness is not something foreign to people who don't have SA. We are all wired to experience shyness (except psychopaths) at some point or another.
Shyness also has nothing to do with energy levels. When you get into energy levels, you're talking about extroversion vs. introversion. Both extroverts and introverts can experience shyness and social anxiety, though I imagine it would be much more difficult for an extrovert to have the disorder. Introverts who lose energy through socialization can also rarely feel shy. They just tend to be reserved to keep their energy, whereas a shy person would be reserved because of the anxiety they are feeling.