this one makes me think of mean girls every time
In the uk a bun is a sweet thing. We would call it a bread roll or a bap.
That very much depends on your location in the UK. I grew up in Newcastle upon Tyne and bread rolls were 'bread buns'.
"Did you've butter on your bun?" doesn't make sense :-/
Duolingo sometimes makes automatic contractions and expansions with certain words (mostly with personal pronouns). It's often helpful, so you don't have to enter both "I'm" and "I am" into the answer set, but sometimes makes for awkward sentences.
Is a bolle the same as a roll? The translation only says 'bun'. We (US English) would use 'bun' for more of sweet roll type of thing, I think. Like cinnamon buns. Caramel buns. etc.
Bolle refers to a bread roll, yes.
In other exercises Duo accepts both
Hamburger buns and hot dog buns are not sweet, are they?
Pierre, from what I've heard any type of bread in the US is rather sweet compared to what you get in Europe.
Why can't the butter also be in the bun?
Like, a butter-stuffed roll? That would say "i sin bolle".
Can't you say "had you butter on your bun" in english ?
Yes, that is grammatically correct but more rarely used. Thinking about other examples, I find myself avoiding the simple past most of the time.