It's a somewhat dramatized portrayal of the dress rehearsal for the first public performance. Although composers were increasingly relying on public concerts for income rather than being employed by an aristocratic household to write for a private orchestra (as Haydn was), it was still common for the dress rehearsal to double as a private preview performance at the home of an aristocratic patron, in front of a small audience of invited guests. Often this was regarded as the first performance of a piece, even though the audience understood that they were sitting in on a rehearsal.

Haydn did not in fact attend the dress rehearsal, but he did attend the first public performance. What he says at the end of the film is an amalgam of various comments he made later about the Eroica symphony.