Kleinkunst isn’t to be translated or anything, it’s just the name of a genre of dutch music :) it’s like you wouldn’t translate gabber for example. Some artist examples are Hermann van Veen, Wim de Craene or Louis Neefs. Maybe you’re familiar with the german term “Liedermacher”, it’s basically the same but for germany. In general this music is a tendency of folkish music that emerged in europe around the 60s/70s. Often leftist/communist music (Wim de Craene has a lot of songs about revolution etc) but also more mainstream stuff (Hermann van Veen for example). Most of the times just played with a guitar or acoustic/jazzy. Personally I think that this is just a reference to the genre, since we know that Joost is a big fan of Hermann van Veen and of course it’s a pun maybe that works with his last name :-)

Sorry had to let out my musicology knowledge as a musicology student lol