Obviously you can't use the word all when describing people since everyone is unique. But I will say this. In my experience, I noticed a similar correlation between innocence and freak in bed.
I attribute this two 2 things.
1. Shy girls usually have more pent up sexual tension. One because they aren't exercising their sexuality, and two, due to their shyness, they rarely receiving an sexual tension as well. Guys aren't flirting with them, hooking up with them, or simple showing interest. This makes her sexually frustrated, similar to the guy who hasn't been laid in over a year. Think of it like the caged bird analogy. When you keep a bird caged up long enough, one you finally release it, it starts going nuts, flapping its wings wildly because its taking full advantage of its new found freedom.
2. I think these shy girls tend to be a bit better in bed because they feel they have more to prove. Hot girls, or girls who get lots of male attention, have a tendency to get lazy in bed. Simply put, they are overconfident and feel that their looks alone with sell you and keep you coming back and if not, there are 5 other guys ready to take your place. They don't feel the need to try hard to work at making sure you are happy in bed because she feels she's so hot, you'll won't care. Shy girls who don't get as much male attention feel like they need to try harder to keep you happy because they are insecure. They will go to great lengths to keep you happy in and out of the bedroom for fear of you leaving them. Simply put, hot outgoing girls tend to get spoiled.
No, I'm shy in any situation. So not all shy girls are like this especially virgins. Maybe she's just comfortable with you? But even if I was comfortable with someone, I don't think I would be able to do that easily.
Not all of them are like that. Most people especially shy girls aren't going to be that open when expressing their sexuality. When you have sex with someone you are letting yourself go and opening up to them.
Just thank your lucky stars. Women, like men, can have sort of dual personalities. In public, I try to be the perfect, courtly gentleman. In bed, I'm a dominant, sadistic animal. Some of us just keep our sexual selves separate. Glad you had such a good time. I suspect if the two of you shared some sexual fantasies, you'd open the door to even more mind blowing sex.