Of course the exchange became heated. Don't you get the whole picture? The COI is convened to look for one or more scapegoats to arrow and take the fall. The ground commander knows this. He is being called up to defend himself. And in his mind, he already knows that he is one of the scapegoats that will be sacrificed. He is fighting for his career and professional life. Even if he is wrong, he must also vigourously defend himself or else go down without a fight. Hence you have an argument in court. Don't forget too that these fucks are not used to being interogated like that and hence they get defensive.