I think that's the idea the filmmakers were shooting for. That Mozart was basically an immature frat boy who happened to be blessed with this amazing talent.
Considering he wrote several seriously vulgar bathroom-humor songs I'm guessing it's pretty accurate.
I actually thought the choice to cast Tom Hulce was inspired. I loved the movie, and Mozart was played the way I had read that he was; a genius musically, but flawed otherwise. As he says at one point in the movie:
… I am a vulgar man ! But I assure you, my music is not.
I intially disliked this portayal of Mozart. But i imagine his particular flavour of genius would have been hard to get right: clever but serious, smart but liked a toilet humour.
I do think the actor was guided by the producers ideals to turn Wolfgang into some sort of spoilt gifted frat boy, rather than a hard working musical genius.
According to history he wasn't too far off in capturing him, they say he acted like a petulant child most of the time and got away with it because he was a musical genius.
