Music scene in restaurant is real. The actors are actually playing the instruments and the audio was recorded live, which is rare for a full length film. Typically actors mime their performance and the audio is recorded in a studio.
Doina is a Romanian musical style and a candy bar.
The audio after the credits say "eat your goat dick and shut up!"
Writers describe this film as "a workplace comedy that goes horribly wrong" not a horror movie.
Doina is most definitely a candy bar as well. And actually doesn't taste half bad.