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”.)
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b) A derogatory way to taunt a slightly older person on account of their age, using outdated practices, etc.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.