"Is he not a boy?"
Translation:On není chlapec?
You can perfectly say in Cz "Není chlapec?" and mean "Is he not a boy?". Czech people seldom use on or ona, only if they emphasize it. If that is the case here, you cannot know from the written language.
Please, duolingo, stay out of these controversies. I want to advance in this course because my Czech language level is already moderate and i am stuck here because of these discussions. Není to žadna legrace!