Google lied!
*Enter Google "Quality Update". Now Google has confirmed a change. After more persistent follow-up from industry leaders at Search Engine Land, Google has stated there was an update. Stating "there were chances to its [the algorithm] core ranking algorithm in terms of how it processes quality signals. Digital marketers are calling the update the "Quality Update".
Google's Definition of Quality
As of today, Google has not provided any updates or definitions of what and how the quality update effects websites or how quality is assessed. We know for the last couple of years Google has stressed the importance of quality content for webmasters. For all we know Google could make content ranking factors more or less relevant. Normally when an update occurs, we can see a change at an aggregate level by industry. However no specific industries have came forward saying they have been "hit". Hubpages has suggested and provided data that insists Google was targeting "How To" websites. However looking through that data, their report even shows some contradictions.
All in all if you are a website that has been hit drastically by this update, I suggest you share your case study since the industry does not have much data to go off of. The only thing we can currently assume is if you have seen a minor decrease in traffic, you are probably not the only one. For 2015, the continued theme still remains "content". Build great websites, create great content, and you will be doing better than most in the industry.