Why are some American expats so confident while knowing so little?

Why are some American expats so confident while knowing so little?

I know this may sound like a generalization, so I'll say up front: this isn't about all Americans.
Here in the Philippines, I keep running into a certain type of American expat who has an amazing ability to speak with complete certainty while knowing almost nothing.
Recently I got into an argument with one of them.
I told them I'm a foreigner (European) living here and that I work at an investment bank.
Their response was roughly this: "No, you don't. Investment bankers are in Singapore or Hong Kong."
That was it.
They knew nothing about where I work, what I do, or what my career looks like. Just because I'm in the Philippines, they concluded I must have made up my job.
If they had said, "Singapore and Hong Kong are bigger financial hubs in this region, and most regional finance jobs are concentrated there," that would be fine. A very reasonable statement.
But somehow it went from "Singapore and Hong Kong are bigger financial hubs" to "So there's no way someone doing investment banking is in the Philippines."
What is that…?
Do they think there are no banks in Manila? No M&A, no capital markets, no corporate finance, no major financial institutions? Have they never heard of Makati or BGC?
Do they think the entire Philippine economy consists of sari-sari stores, remittances, and foreigners spending dollars here?
Then it got even more absurd.
After deciding I was lying about my job, they started implying I was hiding some kind of crime. They went from "You're not an investment banker" to, quite literally, me wearing an orange prison jumpsuit and doing terrible things to vulnerable people.
Sorry, but how does someone get there?
Their logic went like this:
I live in the Philippines.
Investment bankers are usually in Singapore or Hong Kong.
So you're lying.
So you're hiding some criminal activity.
What bothered me wasn't that they were wrong. Anyone can be wrong.
It was the confidence.
That absolute certainty displayed while knowing almost nothing.
And I've kept seeing this from a certain type of expat here. Whether they live on a pension, savings, or remote income doesn't matter to me. Some came because it's cheap, some came because of a girlfriend or wife. Honestly, I don't care. Anyone can live wherever they want.
But some seem to spend years inside a small expat bubble and somehow become convinced they understand the Philippines better than anyone else.
They don't know the country's professional class, they don't know corporate life here, and they don't know the local economy beyond what they've personally seen.
Yet they state huge claims with total certainty.
That's the part I find fascinating.
It's not ignorance.
It's confident ignorance.
Being wrong is normal. But being wrong, not checking, accusing the other person of lying, and inventing a criminal story in your head because reality doesn't match your assumptions is a different problem.
Maybe it's just an expat phenomenon, maybe it's an American communication style, or maybe I've just met too many clueless people.
Still, I'm genuinely curious whether others here have noticed the same thing.