What a story. A monk goes to see a Metallica concert (not a classical musical concert), and gets impressed by the 'music'. He remains a monk (including wearing a habit), but also becomes a member of a heavy metal band, being the lead singer, is not retiring. Given the curiosity value of a monk becoming the lead singer of a heavy metal band, he became famous. He is not retiring because of any disputes, but because it looks like the head-banging affected him, and is claiming that he is retiring because of the devil. The devil apparently made him famous to break him away from his friends, and from his band members, and hence the retirement (link to article):
The white-bearded Cesare Bonizzi, a Capuchin who recorded CDs for a punk label and was the lead singer for the band Fratello Metallo (Metal Brother), said the devil was up to his usual mischief.
"The devil has separated me from my managers, risked making me break up with my band colleagues and also risked making me break up with my fellow monks. He lifted me up to the point where I become a celebrity and now I want to kill him," the monk said in his farewell video.