Most of the preset songs combine melody tracks with accompaniment tracks, just like when you record a user song using a style. The manual refers to these as "songs that include chord data" (see page 50, in the last sentence of the "Listen to the DEMO Song for Easy Song Arranger" section). The "Song List" on page 41 has a "CHORD" label next to the song number to indicate the songs which include chord data. This is why you can play those songs using different styles to change how they sound. See "Change a Song's Style" on pages 50 - 51 of the Owner's Manual for more information about this.
What you can do is press the [EASY SONG ARRANGER] button and select the song you're interested in ("003 Chillin"), then press the [EASY SONG ARRANGER] button again to see which style is being used.
