Google has been messing around with the titles displayed in the search results forever. We've covered the topic here several times but it seems with with a recent Google change, Google is more likely to show a different title that what your title tag displays.
Googler, Gary Illyes, said in a Google Webmaster Help thread that often Google is able to pick a better title for the search query than what your title tag reads. He wrote:
Often a single title might not be the best one to show for all queries for a page, so our algorithms may generate alternative titles to make it easier for our users to recognize relevant pages. If you recently changed the content of your page and its title, it may take some time for our algorithms to notice it. While we can't guarantee that your new title will be used, if it's descriptive, informative, there's a fair chance it will be.
Is Google trying to be too smart? Should Google be messing with your title tags? Many SEOs would say they shouldn't be doing this but what Google thinks is best for the searcher is not what SEOs would always believe.