The riff in the video uses the first and second strings on the 5th fret, and on the 8th fret. It comes directly out of the A pentatonic minor scale.
Learning how to mix your rhythms and riffs is a tremendously rewarding skill on the guitar, and the lesson above is just a tiny sample of what you'll learn in Rhythms & Riffs of Early Rock & Roll. If that style of playing appeals to you, I'd recommend checking out the course!