Well, it's often obvious, many people introduce themselves as "I'm from Kansas" or "I'm from New York", and expect you to fill in the blanks, which would never work with "Yorkshire" or "Brandenburg".

Because the country is in North America, not meaning that it is the totality of America (just like United Arab Emirates, although many other countries are indeed "Arab"), which is three different landmasses (North, Central and South). It boggles my how justify this but call any person from the Koreas, Japan, China, the Philipines, Vietnam, Thailand (you get the point) "Asians", when any person born in said continent is also Asian, and not just Oriental peoples. So yeah, you can call your country America (the name of three whole landmasses) but at the same time label as just "Europeans" and "Africans" people born in said continents that have many countries and rarely acknowledging them as such (particularly with Africa), but also feeling pride in your European heritage by calling yourselves Americans because of how (insert Eorpean specific nationality here) you claim to be, because an Bostonian "Irish" seems to be even more Irish than actual Irish people. Anyway, I'll start claiming I live in the US since I live in the "Estados Unidos Mexicanos" or "Mexican United States" (the country's official name which can in fact be claimed by the country because it was given to just the region of what used to be Mesoamerica, later on the viceroyalty of New Spain). EDIT: Not correcting my many typos, they're because I'm clumsy with a keyboard, not because my non-native English isn't good enough or anything of the sort.

Residents of what is now the US were being called 'Americans' by Europeans since before the Revolution.

Go to Mexico. They consider themselves to be Americans too. And they live in the States. Mexico is made up of states. If you are from USA, you tell them you are North American. I still love how many places say Usa (Oosa) instead of U. S. A.

In the two right maps I think the grey bit is Guyana (official language English), Suriname (official language Dutch), and French Guiana (French territory), so none of these are related to Portugal or Spain (i.e., the Iberian Peninsular => Iberoamerica). However, Belize (English speaking, up in Central America) appears to be coloured green (although it's kind of small, so hard to tell). Not sure what the drawer of this map means by 'Latinoamerica'---I'd probably not include the English and Dutch speakers, but include the French speakers since French is a Latin-derived language.

Probably because it's still the territory of France

I believe Guyana is still a French colony.

I have been told that many places in the world do not make a distinction between North and South America. It's just America.

In general, I don't think nationality has much influence on ignorance (with a couple exceptions). However, this can be confusing as the difference between Latin American, Hispanic, and Ibero American is slight but important, and many people refer to the USA as `America`, which of course is incorrect