My initial thoughts are that it was empty and seeing the way the game was going, he knew if he milks it, paok can get the points outside the pitch. Hell if villafanez milked it, we may have just got the game also.
Regardless, assessing the severity of the incidents is not the way to go about it. The moment something is thrown, game over. These idiots continue to throw s%$#! because they are well aware of the possibility that their respective team can get away with merely a small fine.