I think it is because the game itself cost currently 20€, but "Daedalic - Gigantic Bundle" (which contains the game) is currently at 18€.
-> this causes the game to be calculated as much worth as the bundle. which is 120€.
when the bundle goes back to the old price, this game goes to ~18p. (so it is just temporary)

is it a bug ... is it a feature .... I call it the "new reality studio feature" other call it "daedalic bug" (because it happens often with this publishers).

is strange, but legit.

EDIT: it is a steam thing, other sites suffer from the same problem.

... ich besorg mal ne halsstütze.