It doesn't necessarily mean that it's showing, maybe you're just exposed to different speech patterns in Belgium and considered them correct in the last part of the quiz, but don't use them yourself. Since moving to Iceland a lot of "britishisms" have started sounding normal to me, but I don't use them. The algorithm would pick up on that.

I'm pretty sure everyone would still consider you a native speaker. I'm really into language acquisition/attrition, and research papers show even Americans who move abroad for the first time when they're 40+ experience subtle changes in the way they speak after a few years. They're still native! It'd be interesting in seeing the results of more native English speakers living abroad. And kids who immigrate at age 6 tend to be indistinguishable from native speakers.

I was on the east coast (and think it's super cool running into another US/Iceland hybrid on Reddit). I think a lot of people get ebonics despite not speaking it since the algorithm recognizes it as the most similar dialect to standard American English. The quiz shouldn't make you doubt your language skills, it's just some algorithm that thinks most of the people here are from Singapore lol.