Not a blunder at all. Had he stayed at PAOK he would hardly get any playing time. And if he did by any chance and scored the same goals as he did in Germany, the "Liverpools" of of the world would not offer more than 2-3 mil for the player.
If we believe the rumors Nurenberg will pay the 18 mil option + the 2 mil option to get the 85% of the player, then PAOK stands to make somewhere between 23 to 25 mil. Also lets not forget that for Nurenberg to pay the option, the player has to agree to it. What's stopping PAOK and the player to agree and then sell him directly to Liverpool for 30 mil in the summer, taking the middleman out of the equation.