Knowing where JKS has gotten the impetus for this thread from, perhaps some clarification. I don't think he's talking about the idea of an instructor being seen as definitively authoritative in their martial arts field, but outside of that, wanting, or trying to be seen as experts in other areas, such as history, physics, anything, really. Now, if they're actually educated in that area, sure, but there are instances where instructors really don't know what they're talking about, or make fundamental mistakes when discussing such topics, but what is said is taken as completely valid and correct. Kinda like a martial arts instructor telling the class that the reason the sky is blue is due to giant blue lamps on satelites orbiting the Earth (although not usually such a clever deception.... )
As to where it comes from, at least in the case of Japanese systems, there is an undercurrent of cultural beliefs from both sides coming into it. From a Japanese perspective, the core of teaching is made up of a few basic principles: Believe what you're told, Do what you're told, and Don't question what you're told. What this means is that, from a Japanese perspective, students aren't expected to ask many questions. It's assumed that if your instructor doesn't tell you something, you don't need to know it yet. Additionally, asking questions where the teacher doesn't know the answer can potentially embarrass them, causing a loss of face. The big problem occurs when Westerners make up the vast majority of students... as our education system teaches us to ask questions, and seek clarification. And we're used to getting answers when we ask.
Typically, there are two different responces that can happen. The first is that the instructor will attempt to answer the question (in order to not be seen as not informed), but will get increasingly frustrated, and stop answering, just telling you to train. The other is that, if the answers are accepted, the instructor will simply keep answering, whether or not they actually know the answers. This can heighten the way the instructor is seen by the students (as always having the answers), which leads to less questioning of answers in the future, creating a cycle.
What can be done? Well, simply, a little critical thinking. I encourage my students to question even what I tell them, and deliberately give incorrect information from time to time (which is then pointed out, typically after asking who agrees with what I'd said).... with the aim being that they have to understand what is being said, which ensures they're paying attention to the lessons, as well as them critically assessing what is presented, and, if it doesn't match what they already know (and I can't demonstrate why the lesson is the way it is), they shouldn't accept it.