Nah, both my English-speaking and Italian-speaking family use "uncle" and "aunt" with a similar amount of ambiguity. It's a term of respect for elder family members, extended or otherwise.
Meanwhile, I refer to one of my father’s second cousins as my uncle. It completely depends on context, even in more strict cultures around this. If someone is close enough to the family they can be an aunt or uncle even if their relation is more distant.
I'm a bit surprised you've never heard of the spouse of a parental sibling called an uncle as well. To make that more explicit: my father's sister is my aunt, and her husband is my uncle.
That's a bad analogy that's missing context. I have a very close friend of my dad's that I called "Uncle Bob" when growing up. That's very different than reading a news article that says "Famous Person X is Famous Person Y's uncle" - in that context I would expect a very specific set of possible relationships.
At the very least, we can agree that using "uncle" like this is incredibly easily misinterpreted.