All of the things she is saying make sense to his mind, and are correct - he most certainly would untie her if she felt uncomfortable or threatened, and with her talons (among other magic) she could easily free herself if she desired to do so.

"The same would apply to me, I would think," he says. "Even though I believe it would be harder to free myself...I cannot shift my talons quite as freely as you are able. But if I was uncomfortable...I would trust you to free me."

Trust is clearly a large portion of the entire exercise.

"What does...what does it say their reasoning is?"