YOU OFFENDED THE GODZ OF HUBDOM!!!!!!!!!!!!!!!!!!!!!
I'm joking. You did nothing wrong. I promise that I answer this sort of question at least twice a week.
You're author score is based on factors that nobody but hubstaff knows, and they aren't telling anyone.
My best guess, and everyone else's best guess is that author score is based in site participation, and the scores of all your hubs.
So if you wanna have a 100 - don't ask me, I've never been there, but I've been to 97, for like a minute - and then someone on staff said, "WTF?" and bumped me back down where I belong.
Ask and answer questions, hop hubs, comment hubs with GOOD comments, make a trip to the forums every once in a while, vote hubs up or down, flag inappropriate hubs that look like spam, or like the author can't really write in English.
Your author score is always going to be going up and down, it's not important.