To not do that is commonly associated with things like being on the spectrum or cognitive deficiencies.
Judging someone's external "involuntary cues" is not interrogating their internal state. It is, as you said, judging their response (a synonym for "answer") - and that judgment is also highly imperfect.
(It's worth noting that focusing so much on the someone's body language and tone that you ignore the actual words they said is a communication issue associated with not being on the spectrum, or being too allistic)
"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.
You're mistaking the shadow on the cave wall for the thing itself. Inference is not the same as observation.
For the same reason that polygraphs are not lie detectors, the body language that you're convinced is "leaking" is not actually internal state.
