As I mentioned in my other comment, I assumed they were the same, but several sites said they were different things. “American coffee” is a weak brewed coffee, and Caffe Americano (アメリカノ) is a diluted espresso, which is actually stronger than most brewed coffees, at least in terms of caffeine content. Japan has アメリカノ too, and in my experience it’s much more common.
This drink is available in America too, it’s just known by the Italian name, “Caffé Americano”
For the history of why it got that name: https://en.m.wikipedia.org/wiki/Caffè_Americano
As I mentioned in my other comment, I assumed they were the same, but several sites said they were different things. “American coffee” is a weak brewed coffee, and Caffe Americano (アメリカノ) is a diluted espresso, which is actually stronger than most brewed coffees, at least in terms of caffeine content. Japan has アメリカノ too, and in my experience it’s much more common.