There were a few of his companions who remained with him as captives on the ship. While obviously they would be biased in favor of Caesar, there were at least a few witnesses then.

[2.1] First, when the pirates demanded a ransom of twenty talents, Caesar burst out laughing. They did not know, he said, who it was that they had captured, and he volunteered to pay fifty.

[2.2] Then, when he had sent his followers to the various cities in order to raise the money and was left with one friend and two servants among these Cilicians, about the most bloodthirsty people in the world, he treated them so highhandedly that, whenever he wanted to sleep, he would send to them and tell them to stop talking.

[2.3] For thirty-eight days, with the greatest unconcern, he joined in all their games and exercises, just as if he was their leader instead of their prisoner.

Plutarch