They appear to list three guesses for variety of English for everybody who takes the quiz. They correctly spotted that I'm a native speaker of American (standard) English and listed the other two possibilities as Canadian (I do listen to radio from Canada, by rebroadcast on Minnesota Public Radio) and ebonics (which everyone in the United States hears sooner or later).
The guesses for my language background were spot on too. Like many Minnesotans, I have a few dialectal usages that reflect Scandinavian influence, and besides English as a first language, the other two languages guessed for me were Norwegian and Swedish. I have Norwegian ancestry (in part), so I come by those dialect habits honestly.
Hm. It guessed Finnish, Greek and Russian for my native language (German in reality) and a South African/Singaporean/New Zealand accent, where I have no idea how that could have happened – certainly not because I spent any amount of time in these countries (I didn’t) or consumed primarily content originating in these countries (also not the case, maybe apart from LotR…).
Finnish, Greek and Russian also don’t appear to have any connection to other Germanic languages…
Counterdata: I've lived in California my entire life, my only other language exposure in day-to-day life is Spanish, and I have no Norwegian ancestry or local connections. It still thought my second- and third-most likely native languages were Swedish and Norwegian. I'm guessing those languages have ease picking up "native" English.
The guesses for my language background were spot on too. Like many Minnesotans, I have a few dialectal usages that reflect Scandinavian influence, and besides English as a first language, the other two languages guessed for me were Norwegian and Swedish. I have Norwegian ancestry (in part), so I come by those dialect habits honestly.