He is muting every string except for one, which has a note fretted. While strumming all of the strings for that percussive sound. It takes a lot of practice! You will learn more of this in later lessons, although I don't think there is a lesson on the exact playing he was doing.
Also playing some chords with the muting technique. Check out the R37 lessons for some excellent practice ideas to learn this. FT27 (012-4) Practice Routine Starting at 7:30
https://tomovhxtv.vhx.tv/videos/tf-lesson-012-4-practice-routine
Go to that 7:30 to see.
It is not a total beginner technique so it seems like a lot to play this way at first.
I Love the sound of this muted lick he plays. I am so happy to help you find this lesson, as I am just recently learning this technique too.