View the full lesson at Arpeggios: Why? How? Which? When? | JustinGuitar
but how is it possible to pluck so many of those strings in a row?
My understanding is that, you do not need to pluck all the notes, just pick those which sounds good to you and arrange them in a melodic sequence.
Note - Read the section under the “Learn More” tab. A lot more is explained there - past what Justin teaches in the video. It will make even more sense with the added reading.