How come Graves E says it loses a second for every auto but doesn't on turrets/inhibitors?

So basically with Graves E passive, if you auto an enemy, it gets its cooldown reduced by 1 second, as it says when you play him in game.

But when I was autoing turrets and inhibs, this wasn't the case, is this intended or is it a bug?

And if it is intended, can the tooltip in game be changed to accomadate that? It seems really weird.