I know it's the accepted norm nowadays for children to call adults by their first names, so I can see why some think it creepy for children to call people they barely know 'auntie' and 'uncle' but I personally don't see anything too strange in it.
In the 'old days' there was a certain formality between people - everyone would say 'Mr. ___ 'or 'Mrs. ___ ' when addressing or referring to somebody - sometimes even when they knew that person quite well! Over time there's been an eroding of that 'stuffiness' (fortunately), but I still feel there should be a healthy respect or formality between children and unrelated adults - call me old-fashioned.
In a close community - especially one that is supposed to be like one big family anyway - how do you teach children to address adults in an appropriately respectful manner? 'Bro. ___' or 'Sister ___' is OK, but can still be too stuffy-sounding or precocious for a child, and only using first names can be overly familiar, so 'Uncle ___' or 'Auntie ___' is a compromise. That's all there is to it.
The terms 'uncle' and 'auntie' only become weird or sinister in contexts where the 'uncle' and 'auntie' are out to manipulate, control and harm the child.