When I was growing up I could never, ever, ever understand why in the name of Satan, Crom Dubh, Tartarus and dead baby wombats folk abroad kept mistaking Scotland for Ireland. I could not fathom it. I barely can to this day. To me at that age it was like France and China, we are so different. It just didn't make sense. It was even worse when they confused the accents - like a Jamaican accent being mistaken with an accent from Maine or something.
Were most people who did this from the US? Most of us don't even know which of the 50 states are where. Hell, I still sometimes get mixed up with the west even though they're just large blocks. Just never really cared enough to sit down and memorize them. I bet a lot of Americans aren't even sure if the UK is an island or not. We learn the continents, their general shapes, the shape of the US and the 50 states (and then promptly forget them because it's a hassle to memorize). European geography? Please. I'd best most Americans know that Scotland and Ireland are around the UK (Yes, the UK, because UK = Great Britain = Britain = England. It's interchangeable, right?), and there's two islands there, so one is the UK and the other is... both Scotland and Ireland? Sometimes Wales is mentioned or the Celts because movies, but who the fuck knows if that's even real? There's only two islands, you can't juggle like 6 different countries between them, that's just weird and hard to remember.
The thing with the accents is because Scotch-Irish is a thing in the States, and regardless of what that actually means in terms of history and accent, what it obviously means is that Scottish and Irish accents are similar, yeah? Because there's a thing with both of them together. They don't sound French, they don't sound Mexican (Spain exists, but do they really even speak Spanish? Do they have brown skin, too?), they don't sound *Eastern European* (Start at Belgium and Luxembourg, and go North and East through Scandinavia, Switzerland and Germany until you hit Russia, then go south to Greece and east to the rest of Russia. They all sound about the same, yeah?), they don't sound Indian and they don't sound Asian. The closest thing they're to is probably that silly British accent and their difficulty to spell words correctly. They aren't British though, so... Scotch-Irish?
It also doesn't help that we're not exposed nearly enough to the accents so we can't really differentiate. When all our memory is working on is some person we heard on TV like 5 months ago and you sound like you're from around Britain but you're not British... Scotch-Irish?