CPC is not a real metric. For affiliate networks including Adsense, everything revolves around CPM. So basically if you incrase your CTR your CPC is going to increase subsequently. If for example you had autoads configured, they might have guessed where the best clicks are comming from and they might have improved in efficiency.
When people ask this kind of things, it is clear that they don't use the right tools to improve and manage their ad stock (like A/B testing, heatmaps, etc). They just set up the ads and happy to go. And now this questions appear. When the price increases everyone is happy, but when the next month it drops back to $0.3 you will come asking the question, the other way around, just because of this lack of information.