The text is probably mocking Smetana's own description of his tone poem about the River Vltava (DE: River Moldau), part of a suite of six pieces with a Czech nationalistic theme.
Here are the words, taken from the Wikipedia article about the piece:
"The composition describes the course of the Vltava, starting from
the two small springs, the Cold and Warm Vltava, to the unification of
both streams into a single current, the course of the Vltava through
woods and meadows, through landscapes where a farmer's wedding is
celebrated, the round dance of the mermaids in the night's moonshine:
on the nearby rocks loom proud castles, palaces and ruins aloft. The
Vltava swirls into the St John's Rapids; then it widens and flows
toward Prague, past the Vyšehrad, and then majestically vanishes into
the distance, ending at the Labe (or Elbe, in German)."
These words or a version of them are often used in program notes or as a verbal introduction to the piece. The text may also be mocking other program notes which try to make (too) specific associations between the music and some external object,place or person.
On a more practical basis, a tone poem usually takes some theme outside of music - a fictional character, a place etc. The River Vltava is a major river, seen as the national river of Czechoslovakia, so fits with a nationalistic theme. The River Oder is much longer and runs through Czechoslovakia, Poland, and Germany. It may have associations suitable for a tone poem, but less likely.
