"Everyone in the department calls him that."
Translation:Todos lo llaman así en la facultad.
'todos en la seccion lo llaman asi' means -everyone in the department calls him that ( way ) - and this emphasizes everyone who is in the department. But Duo's answer: Todos lo llaman asi en la facultad. This emphasizes everyone calls him that way just in the department. Outside the department they don't call him like that. There is a little difference between the two answers and I believe it should be the number one which should be accepted