Dave couldn't believe what he was reading, Hasan was coming to kill him, and that too for that deer, the way he acted while sitting with him, he would have never guessed in a million years what that giant was up to. He knew that the deer was valuable, but he figured he was successful in selling his story, and the giant believed that he left the carcass behind.
The message also made him realize that Hasan was a very good actor, at that time, he really thought that the giant believed him. If it weren't for this message, Hasan would have been successful in catching him off guard. But at the back of his mind, he also wondered whether this message was a trap.