"He does not like to work in groups."
Translation:Han tycker inte om att arbeta i grupp.
Swedish just prefers it that way, saying "arbeta i grupp" meaning group in a very general sense rather than a certain group.
Compare it to "Switch buses" where English preferes the plural, but Swedish just says "Byta buss" in singular. It's just how the languages say it. :)
If it was really Hon tycker inte om att arbeta i grupper, it tricked you on hon vs han. Since Han tycker inte om att arbeta i grupper is an accepted answer (just not the "best" one) it should never be shown as a correct answer in a multiple choice question. Not that things like that haven't been known to happen anyway.
Personally I hate the multiple choice questions. We can't control what the wrong answers are, they're all randomly generated, so they often end up being either ludicrously easy or tricky in a way that isn't helpful.