I'm disappointed that this turned into sort of a hateful thread about people assuming that the OP is about people who think that they are more _____ than others (although I guess it may have started to evolve into that in the posts that followed. But I think that this may have been a self-fulfilling prophecy more than anything). I believe that all throughout history, staying quiet and keeping one's cards close to one's chest have been relevant to survival.
"Playing dumb," or perhaps "acting drunk" are probably unfortunate choices of words which describe this staying quiet in order to preserve oneself. Introverts just aren't going to be able to say what's on their mind very often. It costs too much energy, but also it is dangerous to throw out too many controversial ideas in an analytical format if one is not in a setting or before an audience that will be open to that. There are too many kinds of people in the world who do just want to look good in front of people at any cost. But we do feel uneasy about others' possibly having more knowledge than us if this knowledge doesn't fit our perception of what each others' status is. Slaves often couldn't appear to know too much (couldn't let others know they could read), women were sometimes considered "manly" or unmarriageable if they read too much or were educated, and I often overhear or directly talk with people who refer to women with careers in engineering or other STEM fields as odd, unusual, or weird. But in contrast, people light up when I tell them I do theatre or art or music. This is a gender thing, but I also believe that this is connected with power, and the language people use and their reasons for wanting to use it.
Ti and its sharpness, its preference for specificity in word choice, its love of jargon and the risk that someone's emotional state may be ignored is extremely off-putting to many. This may be instinctive, or related to misreading patterns from the past. Remaining quiet, passive or silly helps the introvert to rebuild energy and discharge it in a venue that may be more appropriate than, for example, my being approached by an elderly couple on the bus who ask me, "Wouldn't you rather look out the window? Cell phones are an addiction. Don't you get sick looking at that all the time?" It's a lot more energy-efficient for me to just smile and nod, sensing that they might mainly be expressing how they caught up in a high state of emotional arousal at reuniting with each other and going on a day trip together, and to put away my phone, than it is to express in full Ti style that I believe we are moving into an era in which we are becoming cyborgs, and that even now, we can't live our lives without a minimum of technology- like smart phones. All our jobs and educations hinge on the ability to intertwine ourselves smoothly with current technology. Maybe I could learn something cool from hearing their response, but I don't think they are in Ti mode, so it's pointless. I believe I'd squish their sense of ephemeral wonder if I engaged my main function. So I think it's often mean or a little bit selfish to say exactly what one is thinking, especially when that is generally not the reason why most people want to talk with each other or interact.
I generally want to interact in order to acquire new information (Ne), or exchange fun or new and novel information, but people don't often seem to understand that motivation unless it is couched in a lot of eye blinking or submissive curiosity and feeliness. I'd much rather just download the information out of them, but that is too much Ti Ne to operate in a fair, effective way in the real world. This is still about status and the flow of power, but Ti is also hard to digest unless enough care is taken to communicate it clearly for a broad audience. Maybe it costs too much to decode for some. And also, it's extremely hard to know when you yourself are wrong since it's easy to misinterpret patterns from the past and project them inaccurately into the present. Maybe your ideas are terrible, or communicated poorly, not misunderstood. But being misunderstood when you end up being right creates a lot of uncertainty in these matters.
Knowledge is still an emotional, highly charged power thing at times. Not all the time, certainly, but definitely sometimes, and it's really helpful to notice when the discussion becomes less an exchange of ideas and more of a power struggle. Sometimes, we just have to laugh at the boss's joke, we have to smile and nod while the crazy homeless person talks about how he stabbed someone 10 years ago, we have to let go of how we question whether someone just said something accurate in order to let them finish and get their points across. And most of the time, it seems like the point is just to connect with another human being and feel less like one is alone as one goes through the world. So sometimes, it's wiser to be silly and play dumb. Maybe that's closer to the meaning of our social lives. But it amplifies universal human issues with authenticity for an introverted intuitive perceiver. And that shouldn't be treated too reductively. It has very little to do with intelligence.