When music played on a phonograph is sped up, the music should increase in pitch. For example, a baritone singer would sound like a chipmunk, when a record is accelerated. But in this case, it's only the tempo that is increased.
When the two guys dance on stage, they end up stumbling because someone sped up the phonograph. But the phonograph, which can be seen in the background, shows no one touching it when the music accelerate.