http://www.techradar.com/news/google-is-siris-favorite-search-engine-again

Poor Bing. Microsoft's underdog search engine used to have a quiet home on iOS and Spotlight for the Mac, but Apple today said in a statement to TechCrunch that it's parting ways with Bing for most search services. 

Basically, this means that when Siri gives you a list of search results rather than answering your question directly, it'll be creating the list with Google rather than Bing.