I've had okay luck using GK for penalty, corner, and free kicks. He's not involved now, but it's not uncommon.

Since we don't know the mechanics, I can believe those set pieces classmate differently, and by moving GK up to an attacking position, it bumps up the attacking team stat as a whole. It also seems she, might not be, because the game animation never connects the end of a set piece with a dull counter attack.