How inauthentic materials promote critical thinking

Although I would describe myself as an open-minded teacher, I must admit that there's usually 'the' answer (not 'an' answer) I expect to hear from my students. Not that I utterly reject an 'incorrect' response but I usually imply (more or less explicitly) that the student might consider changing or re-structuring the sentence (to fit my expectations). I do this because I honestly believe that this type of control is for the sake of students' linguistic development.

However, most of the time I'm truly amazed at all the unexpected ideas and objections my students come up with in the lessons. The other day we read about orphan bears in our Project 4 coursebooks. It's all based on a true story (which I'm discovering now as I'm typing this post) but I suppose the text itself was invented (or simplified) for the purposes of the EFL classroom. The leaflet, in the form of a letter, is followed by a commonplace matching exercise (words and their definitions). Surprisingly, two of the definitions almost caused a riot among my students. The word fur is described as a bear's hair and den is defined as a bear's home. These are perfectly acceptable definitions for me and there's no reason why I should doubt their correctness. But in the class of 13-year-olds there is a keen biologist (let's call him John). This boy has an enormous knowledge of all the flora and fauna and when I don't know how long a bear hibernates, I ask him. After finishing the exercise, the boy suddenly puts up his hand, outraged. I'm not surprised; it's his usual way of disagreeing with facts. Here is a shortened transcript of the conversation.

John (in an excited way): I've never heard a bigger lie! The author of the book tries to deceive us.
Me (amused and curious): Really? Why do you think so, John?
John: The definitions are completely wrong! Or at least incomplete!
All the students look puzzled but amused. This is like John.
John: A den is the shelter of any wild animal, not just a bear's! And fur is not just a bear's hair!
Me: Hmm. An interesting point.
Students: But, John, we're talking about orphan bears, that's why the definitions are so specific.
John: I don't care. The definitions are incomplete. What a disgrace!
Me: You can write a letter of complaint to the author. Really. Here's the template (I point to the letter in the book).
Students: Yes! Tom Hutchinson. You can write to Tom Hutchinson. But the problem is that there is no address.
John seriously starts looking for the address at the back of the book.
I am speechless because I'm amazed at his critical thinking skills and his courage to speak up in front of the teacher and all the classmates.
Finally, John calms down. However, later on during the pair work, he stubbornly changes the two definitions to fit his idea of what fur and hair are, stressing the underlined words: this is a mammal's hair.... and this is an animal's home ....

I should add that most of the conversation in the transcript was conducted in English (I only slightly paraphrased it) and it makes me think: isn't this is an excellent way of turning an inauthentic material into an authentic activity? Teaching 'plugged' can suddenly change into teaching 'unplugged'. However, it was not me who incited this change. It was John's courage and his need to air views. Now that I think about it, we might try to write the letter together after all, no matter if we eventually send it or not. But I'm sure Tom Hutchinson would be pleased to learn about John's little observation because this incident shows that kids can think critically, even with a coursebook.