In India, at least in Hindi, there is uncle and aunti for strangers and the blood relatives have their own words (mama - brother of mother, masi - sister of mother, bua - sister of father, etc). Whether these specific words are used for non-blood relatives is kinda specific to the people in question.

So I wouldn't say there is any implicit kinship there. If I call a random stranger "uncle" then there's no real meaning to it. If I call him "mama" or "chacha" then that would be implying a relationship.