Yes there is a biggest Google update dont know panda or penguin. But number of websites have been effected by this update. My website got the first page position after that update.
So you got first page position after this update.congrats buddy.Maybe your page content is good and original.
I've noticed, based upon the two KW Tools I use, that it seems Google is ranking the keywords more towards the AdSense usage vs. Free or viral. That's why I rarely pay much attention to Google's KW tool any more, unless it has to do with a paid add campaign I'm running. I just use my two favorite tools.