Difficult as it is to recall now, 2009 was a period of relatively subdued inflation, because of the deflationary impact of recession: taxes and benefits were uprated by an inflation rate which then turned out to be much higher than what actually happened to prices in the subsequent 12 months.
Stocks could go down further and commodities may repeat their break from 2008, especially if the world goes back into a recession and would bring a deflationary environment.
Bernanke knew that if the economy did slip back into recession, the country ran the risk of entering a deflationary spiral, which once started, is awfully hard to stop.