Nationality is where you were born, not where your (grand)parents were born
I find it annoying when people describe themselves as Irish or Italian or African, when they weren't born there, when they've never even set foot in that country their entire lives. It's their parents who were born there, or in some cases it wasn't even their parents, it was their grandparents or great grandparents who were born there.
If they grew up in that country or if they've been living there for years, then I could understand. But they haven't even been there! But even then I think your nationality is still where you were born. For example I've been living in Ireland since I was 3, but I was born in England, so therefore I'm English.