(V. S. RAMACHANDRAN)
The author/researcher says he believes that is one of the main mechanisms of human learning (babies look at adults and imitate. Adults look at other adults and imitate. Subconsciously)
What you are describing sounds very similar.
At some point the child gets old enough that you start to feed them 'baby food' on a spoon. The child isn't used to eating off of a spoon so for many weeks the process is messy. The initial challenge is getting them to open their mouth wide enough for the spoon to enter. And telling them 'open your mouth' is not particularly useful since they don't understand English at that age.
Instead, the following instinct kicks in: as you approach their mouth with the spoon, your own mouth opens. They see your mouth open and then open theirs. The crazy part is that your own mouth opening happens involuntarily at the moment you want their mouth to open. It is difficult to suppress it if you try.
I've also noticed the reverse. When the child gets a little older, they at some point want you to open your mouth, because they want to feed you something or they are curious about the inside of your mouth (this is a phase they go through). They seem to also involuntarily open their mouth wide when they want you to open yours.
Negative reinforcement is what boot camp uses. If you square your corners, you won't get shouted at. The "negative" aspect relates to the lack of shouting, and the reinforcement relates to the fact that the shouting is unpleasant.
At home, positive punishment would be making fun of the tendencies, and negative punishment would have meant receiving no validation for the behaviour.
Before social media, there were movies that molded society. Bollywood and more recently K-dramas/K-pop have influenced an entire generation.
Often these were used for shaping a younger generation as a long term strategy for a desirable adult demographic. To a certain extent, it is happening in our American public school system. Everyone who comes through it are kind of identical. It may not be apparent to those who have never stepped out of the States, but it is obvious to those outside or have known other cultures.
With social media impacts, its effect is like an oil spill. Even if you can contain it, it will be messy, expensive and traumatic for years and years. This is a Faustian bargain we have made.
As someone who moved to the US in his mid-teens (from a non-english-speaking country), that's quite literally me with British movies.
After watching a few over a weekend, Mondays are usually rough, as I end up saying random words in British accent and immediately correcting myself.
If someone spends many hours a day watching someone with particular quirks, it doesn't seem surprising (drawing parallels here to my experience) that those quirks may transfer because their brain starts to make those associations through observation. I would expect that stopping watching that particular person would probably let the transferred tics decay over a period of time (I'd give it a month).