Fake expertise by pleading (occasional) ignorance

The nice man from Tokyo Gas came today to turn on the stove and hot water at the place I'll be staying for the next two weeks or so.  I used one of my patented tricks on him, something that works every time to convince Japanese people that I am Wonder Gaijin, capable of linguistic feats that absolutely transcend the humanly possible.  This is also, importantly, a method that can be applied in a wide variety of situations, and which speaks to some deep function of human intersubjectivity.

It works like this.  The gas guy (or any given Japanese person) is talking a blue streak at me, which usually happens pretty quickly after I greet them with a reasonably confident "Konichi wa" and explain to them that "I don't speak much Japanese" in decent Japanese.  I do not understand much, if any, of the specifics of what he's explaining to me.  But about halfway through the chat I pick out a word - you can pick out pretty much any word, you don't understand any of them, remember - and stopped him, puzzled.  I repeated the word a couple of times, then went to grab my dictionary.  I figured out what the word was, made a slight "o" of recognition while nodding gently, then looked at him, cueing him to continue.  I then proceeded to not understand the bulk of what followed.

As he was leaving, the mechanic told me that in the entire time he'd been working the job, I was the best Japanese-speaking foreigner he'd met.  At least, I think that's what he said.

The lesson here is pretty simple.  If you make a big, ostentatious deal out of not understanding one very specific element of a conversation, presentation, or what have you, then your interlocutor is likely to assume that you understood everything else that they said.  It's a misdirection, a slight-of-tongue, a gaslighting - the one point of misunderstanding effectively distracts from even the possibility that you didn't understand anything else being said, either.  This could be an effective tool/weapon in, say, a graduate classroom ("What exactly do you mean by gradation?") or a boardroom ("I'm not sure I'm following your point about ISO ratings.").  I hope all of you use this insight responsibly, but I'm more concerned with the deeper structure we're encountering here . . . in precisely what way does a protestation of ignorance make your erstwhile silence seem like comprehension?