Garen attacking from the bush, staying hidden.

Was playing a match and Garen was bot lane as a support, he kept using his little spin and win from the edge of the bush every time Id go to shoo him out, or when I didnt know he was in there. He would sometimes briefly appear, then go back to being hidden.

One time I didnt know he was in there and I just started taking random damage, but the minions wernt hitting me. To my surprise it was Garen in the bush spinning and doing damage, but remaining hidden...

Small thing really, but that cant be acceptable to do any damage from the bush, however short range, and remain hidden.