Some campaign adviser told him that a damaged ear presents as damaged goods, and it would be better to cover it. This is a man so concerned about his looks that he spray paints his face orange. His narcissism elevates the priority of his looks beyond any perceived sympathy (sympathy being a foreign concept to him). Even his rabid base depict him in their artwork as having a six pack abs. He is absolutely covering it up. If the blood was a prop then even his dumb handlers would be smart enough to apply a fake scab to keep the ruse going.