It is two banjos, but I think plays the "melodic" part and there is another player making the back-up accompaniment. Pigtown Fling is not a too difficult tune, and Pete Seeger was absolutely a really good banjo player.
I agree with Jean Louis. It is Pete Seeger playing both banjo parts in Pigtown Fling. I listened to the other tracks on the LP, and in most songs there are multiple instruments. According to the liner notes the recording of the LP took 8 months and were done in the garage of Fred Hellerman (from the Weavers) who had an 8 track recording machine. Pete used to give credit to other musicians so I presume he was the only musician.
In case anyone wants to play something similar but doesn't have Pete's abilities, this is a fun version and easy enough to pick up in about 5 minutes.. The poster goes thru it slow a few times and then takes up speed.