Why? The oscilloscope has an x and y input to control the spot and it's controlled by the sound card output. I'm curious to know what about the explanation you don't find believable.
The explanation leads me to believe they're trying to say that the music you're listening to was fed in to the oscilloscope, and that produced the pretty images and text, which is clearly not what happened.
Thinking about it some more, I suppose they wrote a program to manipulate the soundcard output, but I'm still interested in the specifics.
