These are intervals 1-3-5. Like everything on guitar there are five main octave centers each with its own unique fingerings. If you learn to play the arpeggios for the I IV and V chords you can later use these same shapes in arpeggio progressions.
He also shows you the inversions which sound similar but different enough to matter. Its more fun than mud wrasslin' or roller derby! Especially if you have some effect pedals like delay or a Strymon Big Sky.
Arpeggio usually means a chord treatment as in meaning "play it like its a HARP". So maybe they shortened Harpeggio to arpeggio. I'll bet they did those lazy musicians!
Speaking of lazy, have your pad and pen handy as there is a lot to pay attention to. You'll be glad when you quickly whip these note shapes that he shows us into shape.
I mean Danny tells you the note name but you need to chart it out so you can practice it regularly. That's what I did. In this particular case its not a biggie.
Arpeggios - Danny Gill Page One | Page Two | Page Three | Page Four
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