This music is a term borrowed from... cooking. In fact: the French since ancient times, have a reputation for being the best chefs in the world. And here in French "pot-pourri" - mixed dish. Different mixture.
What is this "mixed dish" in music?
Medley - piece is quite large in size, often orchestral or piano, composed of borrowed melodies.
There are a potpourri on themes from well-known operas and operettas, on the theme of popular songs. You probably had to hear potpourri of songs Dunaevsky or Solovyev-Sedoy. Sometimes they are called fantasies.
The Band "Dr. Watson". School medley