> It is no more confusing to Americans than the fact that Europeans use A4 is to Europeans. Why should it be?
Well, A4 (and variants) are not Europe-specific formats, it's the formats most of the world except some few countries (including the US) use, so I'd say it's slightly more surprising than the other way around.
> Right, but why does that make letter size confusing?
That's the part I initially quoted; "the paper that the text was printed on wasn’t an A4, it was smaller and not a size I was familiar with. I measured it and found that it’s a US letter size paper at about 21.5cm x 27.9cm"
The author isn't from North America, so they had forgotten the format was different, so they got confused when they assumed it would have been A4 like the rest of the world, but it wasn't.
> the only people in the US who would even notice would be people who commonly do business with other countries or who live near the border
Or, as in the case of the author, they live outside of North American and send/receive letters to/from North America.
Right, but why does that make letter size confusing?
Even if every other country in the world used A4, the only people in the US who would even notice would be people who commonly do business with other countries or who live near the border. And in reality, Canada and Mexico also use letter so the border thing doesn’t apply.
So why should letter confuse us just because other people use something else?