A child will simply not be introduced in a familiar way to someone you don't trust or respect - they will be kept away. If the person is referred to for some reason, they'll be referred to as "that person" or somesuch.
When I ask my son to refer to someone as uncle or auntie, it means I'm signalling to him that they have some degree of standing in my life: they are a colleague, or friend, or acquaintance to whom I am asking him to show respect on my behalf.
An uncle or auntie is someone who "is known". By bestowing that title, and instructing your child to use it with them, you are granting them status in the eyes of your child, and segregating them explicitly from the general set of all older people.
When the term is used by adults, it naturally refers to the _even older_ generation of the elderly. So in this case, where the perspective of the writer is an adult perspective, it refers to the elderly.
Lastly, there's a subtle detail that should be made explicit. When it's used "in general" like it is in this title, it does not imply that I, or any reader, considers all of those people uncles and aunties personally. It's implicit in the usage that we are referring to "people who are uncle and aunties for those whom they are the uncles and aunties of".
I hope I've done a half-decent job, because the entire set of cultural associations around that word are hard to get across.
1. It's not necessary, for instance, that the person being referred to by the kid is "known". It's quite common, for example, for kids to address an unknown stranger on the street using "uncle" or "aunty" - it's merely a respectful way of addressing an older person.
2. When used by an adult, it can take on one of two tones:
a) The genuinely respectful tone, similar to (1)
b) A derogatory way to taunt a slightly older person on account of their age, using outdated practices, etc.
The way it's used in THIS article, borders on 2(b) - taunting an older generation for sending good morning messages, etc.
I hadn't personally encountered the 2(b) form you reference. When I was a kid, even an implied taunting of the older generation was forbidden, treated as stepping out of the bounds of social protocol, and would get you punished by your own parents or family if observed.
Even now, as an adult, I would feel strongly compelled to stop myself from using the 2(b) variant you just referenced. It feels taboo.
Maybe things have evolved a bit since I left India, which I admit was quite a while back. I wonder if my grandmother might lament this change as a deterioration of values in the younger generations :) "The kids have no respect these days".
(in addition to the other usages msravi noted)
There are other words used like that, eg “mate”, which can be used in a friendly/neutral or menacing way.
(As a side note - I notice that Kamala Harris’s Twitter Bio currently includes “Auntie”.)
There's such thing in Russian too. My parents had friends and they would come to our apartment every once in a while. We would call them all "uncle $name"
It could be either brother (bhaiyya, anna, chettan ) or Sister (deedi, akka, chechi .. ) if the person is elder to you but not too older than you. So if you are in 20's , and shopkeeper (who is Raju) is in his 40s, you might call him Raju bhaiyya (or Raju anna in Tamil, Raju chettan in Malayalam).
If there is a visible One generation gap, then Uncle or Auntie is used.
And if there is a visible two generation gap, then grandpa and grandma is also suffixed to call them (but this is not very common.. and sometimes could be taken as insult)
And the elders might call you Son or Daughter (beta, beti ..) in a similar way.
And you could be complete strangers.
They could be related to your parents or friends of your parents or a random person on the street who is older. Kids literally walk into mom-and-pop shops and address the shopkeeper as uncle or aunty.
Adults calling other adults "uncle" in Russian sounds either infantile or patronizing. Which is why I assume the Asian usage norms are different.
For me, close relationship people are always assigned as native words. Stranger, in urban setting, are uncle & aunty. Although now kids also call me uncle. Today's kids' usage of native names has shrinked, & more people are now uncle aunty now.
Whatsapp forwards, crazy info like tracking chips in currency notes, cow urine the solution to every pain, indian X is the best X in world, overflowing nationalism, are more from uncle & aunties, who are not good with technology, & got introduced to whatsapp directly.
"Mister" is generally used for someone older and "sir" is usually used for someone around your age. The equivalent mapping in many Asian languages is "mister" = "uncle", and "sir" = "brother".
In the case where you are speaking generally, as in writing an article about some people rather than addressing them directly, then it is sort of subjective and not relative to the speaker's/writer's age, but "older" people (~50-60s onwards) are referred to as "uncle/auntie" and "younger" people are referred to as "brother/sister". What is "older" and "younger" here is a very fuzzy line, and it's possible to offend someone by using the wrong term, but this is pretty universal and not exclusive to Asian languages.
In Russian (and various other languages of Eastern Europe), "uncle" and "aunt" can be used to address a stranger on the street. It comes off as a bit intimate or even childish. It doesn't suggest that the person you're addressing is related to you. If you don't know the name to address someone by, it's less brutish than the alternatives, "hey man" and "hey lady."
For example, in the greatest work of Russian literature (The Twelve Chairs), the main character enters the scene pursued by a street urchin who keeps asking him, "Uncle, gimme ten cents!" The urchin earns the immortal reply, perhaps the best-known line in all of modern prose: "Maybe you also want the keys to the apartment where the money is?"
But this "aunties" and "uncles" seems to be different. I get a sense that it suggests a circle of doting busybody relatives who dance around you all day to attend to your whims as the baby of the family. Or something like that. What does it mean?