All the notes are from a single scale. You pick one of two available scales, the "major" and "minor", which in this case are the Pentatonic major and minor scales respectively. That it has 5 tones is obvious since you might notice that each tone is repeated 5 steps above, in the next octave up.
The reason this scale is so popular for this type of music device - "penatatonic sequencers" - is because it's almost impossible to screw up. So you could describe using the pentatonic scale as removing some of the opportunity for making the music more interesting, but in return you almost completely eliminate any opportunity to make it "sound bad". Any note can follow any note in the pentatonic scale, which is why "randomize" or handing it to a child (which is the same thing) works as a creation method.