How did old man mccalister simms know joe wasn't lying about charlie and ed-rose hunting the night before?

Old Man McCalister Simms knew Joe wasn't lying about Charlie and Ed-Rose hunting the night before because he had firsthand knowledge of their activities. He had been out in the woods himself and had seen the two of them, which confirmed Joe's story. This awareness gave him credibility and understanding of the events, allowing him to recognize that Joe was telling the truth.