From Los Angeles Times article:

The performance was taped in December by visiting Norwegian artist Morten Traavik, who traveled to North Korea to look for musicians to play in an upcoming music festival.

According to one report, Traavik presented the students with a CD of the Euro-pop group. Two days later, the report said, the group surprised him with their improvised version of the song.

Norwegian band A-ha's eternal pop evergreen performed by young accordeon players from K-- Song School of Music, filmed in Pyongyang, North Korea in December 2011. Part of multi-genre project THE PROMISED LAND by director and artist MORTEN TRAAVIK, opening at the international arts and culture festival Barents Spektakel in Kirkenes, Norway February 8-12, 2012 (Juche 101).