Graves critting turrets and inhibitors

So i was in a game of league playing against a graves.He had around 40% crit chance, he starts split pushing and suddently he crits the turret for 707 dmg.... I had seen a video about this when he just got the rework and it seem that he can crit if he attacks something just behind the structure, just like with minions he'll hit the first thing infront of him.