When Rostov sees his hero, the Emperor, he fails to act and I believe this adds to his inner anger at life. But where Andrei meets his, Napoleon, he couldn’t care less. Andrei has glimpsed something greater in life and though he will not have a religious conversion, he does seem to grow cynical and more distant towards all other people because why should any of this matter? All men are insignificant.
I believe his not helping his beloved Emperor is the turning point in Rostov’s life, that moment when onward he will harbor an anger and disappointment with himself. But it’s one of those moments that doesn’t live close to the surface but is hidden like the soldiers falling into the ice at the end of the chapter. The description of the wounded as being like heaps of manure in the field is Rostov’s mindset.