"Do you eat bread?"
Translation:Syöttekö te leipää?
I agree it should be accepted, but not with your reasoning. There is no indication this is just one person either. And even for one person, in Finnish (similar to French and several other languages) you can use the 2nd person plural to be polite, but it's becoming less common. (The opposite of English, where using the more polite plural form even when talking to one person eventually became so common that the singular "thou" fell out of use entirely.)
I've lost lingots on an advancement test because of the poor translations by Duolingo here. It's becoming more a quiz for the right duolingo answer and not the language. It's pretty poor stuff