What is Huck's reason for trying to escape? Do the Duke and King believe him?

Huck says that when the group of men were digging up the corpse a large man had his arm but said that he had pity for him. Apparently he had a boy like Huck that died last year. When the commotion over the gold began, Huck says the man told him to "heel it" (I love that term!) or else he would hang. Huck says that he was so frightened that he ran when he had the chance (not far from the truth!)