Art is a comment on culture. It is often easier for an outsider to comment than it is for someone steeped in that culture. There are no doubt many aspects of American culture that go unnoticed by Americans but are obvious to Canadians.
Also maybe some aspects of geography, like knowing in which continent Canada is.
The average non‐American is from outside the Anglosphere, and so may be from a culture that considers North America and South America to be a single continent. But continents don’t have an objective definition, only a cultural one, and in the language and culture of the Anglosphere the Americas are distinct continents, America is a country, and Americans are that country’s people.
I’ve never met a Canadian who clamored to be called an American. (Except naturalized citizens!)
I usually try to use US-ian instead of American, but it looks really stupid and so I get why it is pretty widespread to call us Americans.