Folk is pretentious? It literally means common people, the opposite of pretentiousness. I am thinking that you don’t have much familiarity with the word nor the people that use it. It does not carry the meaning that you seem to think it does.
You are likely hearing /seeing it being used by people raised in an area where that is common vernacular to casually identify a group of people that share a culture.
My favorite thing about the internet is hearing questions that I would never think to ask and seeing answers like this.
Thank you for helping to make the internet a bit more interesting.