"Nobody interrogates each other's internal states when judging whether someone understands a topic. All we can judge it based on are the words they produce or the actions they take in response to a situation."

I'm fairly sure I wrote something that contradicts these two sentences.

You can commonly figure out whether people are leaking information about how they feel and what emotional and cognitive states they are in, even in text based communication. To some extent you can also decide the internal state of another person, and it's often easier to do with text than in direct communication, i.e. two bodies in the same space.

This idea that people aren't malleable and possible to interrogate without them noticing would be very surprising to anyone making a living from advertising.