He says the tape this song is from is called 'searching for heritage' at the beginning of the video. The very first link when you google that is to the tape by John Butler. The song is by John Butler.
Typically classical guitar players have their nails like that, since they don't use picks. I don't know if this guy is classically trained though, cuz they usually rest the guitar between their legs, not up on their knee like that.
Literally half the web sources I've seen the video linked to labels them as descendants of vikings. All I had to do was google "Árstíðir descendants of vikings", and there's 6 ******* links that have that in the tagline. Do literally any amount of research next time before immediately calling ******** .