According to a contemporary (1946) Universal Studio press release, that Leonard Maltin quotes on page 173 of his book "Of Mice and Magic":
POET AND PEASANT inaugurated an innovation which proved immensely popular. This was the use of classical music by a symphonic orchestra, against which background the cartune [sic] action took place...Based on this press release from that period, it looks as if the success of "The Poet & Peasant" prompted Lantz and Universal to reevaluate this cartoon, and to use the essence of what made this cartoon a hit-the "use of classical music by a symphonic orchestra"-as the basis for a new series built from this concept. From the wording of the release, this new series looks to have been conceived after the release of "The Poet & Peasant"- because the cartoon "proved immensely popular". It looks to be a very conscious decision by the creators to make this cartoon the first of their new music-based series; albeit after it was first released as an "Andy Panda" cartoon.
...So successful was this production that Lantz is making it the first of a new series to be titled MUSICAL MINIATURES.
The second release in the MUSICAL MINIATURES series will be CHOPIN'S MUSICAL MOMENTS [sic]...
Therefore, due to the peculiar, dual-nature of this cartoon; it has been decided by the administrators that "The Poet & Peasant" will be listed here in the BCDB as an "Andy Panda" cartoon as well as a "Musical Miniature." We feel that the cross-referenced listing, with this accompanying text, will remain true to historical fact while at the same time respecting the original creators' intentions.
Thanks to Zavkram for spotting and researching this anomaly.