C'est un garcon bien. Shouldn't "bien" be "bon". The good is connected to boy and not to the verb
Just a general comment: you seem to have reached a point in the lessons where the quality has dropped off sharply, probably because the majority of people don't get that far and so there hasn't been enough feedback yet. Make sure to submit feedback, since you obviously have a good grasp of the language already and your input will be valuable to the beta process.
What milneyj told you, siebolt, is not wrong but I suspect there is something else (haven't been exposed to that exercise yet so I have got to refer to the translation proposed by DuoLingo to get the meaning). 'Un homme bien' is a man with human qualities and moral values, not only a 'good' man, nearly a 'great' man. Actually, it is the exact contrary to 'a bad boy'. In French, a 'bad boy' is 'un mauvais garçon'.