This arrangement uses Thumb Lead, Two Finger style banjo. Thumb lead is a type of two finger banjo where the thumb plays the lead(melody) and fill in notes and pinches on the 5th string. The index finger usually hangs out on the first string. Two finger banjo is much more simple and intuitive for new players than 3 finger banjo, but it can also help an experienced player get new ideas and perspective.
If you check out the licks you'll find some two finger goodies, along with some Scruggs licks. There's even a few single string licks. Single string works great in combination with two finger banjo since most of the time just thumb and index is used to play in both styles.