Translation:A musician is different from an architect.
In Hungarian there is a saying "Architecture is frozen music" therefore the journal of the faculty for architecture of the Budapest Technical University was titled "The Frozen Musician".
Duolingo has asked for the passive voice and your phrase 'differs from' is in the active voice. That's all. I like your phrase, not exactly for this sentence* but Duolingo, anyway, is quite literal.
*Just having another think about the Duolingo sentence, and I think I prefer the passive voice here anyway.
I would think because 'differs from' would be expressed 'si differenzia da'. It does mean the same, but Duo wasn't looking for a verb here.