When the engine cannot be started with the IMA motor
WARNING: This page is about a different car, the 2011 Honda Insight and 2010 Honda Insight. However, it is still accessible from the selected car via links, so may be relevant.
Based on signals from the MCM, when the SOC value drops, when the temperature is low, or when there is a problem with the IMA system, the PCM judges that the engine cannot be started by the IMA, so it is started by the starter motor.