You are miss understanding what he meant. I don't think he meant to explain the reasoning used by the attackers, he is however trying to understand what caused

You are miss understanding what he meant. I don't think he meant to explain the reasoning used by the attackers, he is however trying to understand what caused all these people to start killing in the first place. ISIS surely feeds on religion, but the root cause of the problem is not only religion, just as the root cause of the Crusades wasn't.