I'm not sure this is to ensure the content is made by humans, that isn't the goal. Valve just wants to ensure that the game dev owns the rights of the content created for the game. Using AI, you can still own the rights in some scenario's as long as the AI doesn't use inputs that it doesn't have the rights to.
This is a very good development, it ensures that creators and owners of content are safeguarded, while at the same time ensuring that gamers get fresh and new content.