[GAMEPLAY] Zilean/Guardian bug

In my most recent game, when playing Braum, I took the Zilean Q attachment and it procced my guardian, putting it on cool down. As far as I know, there is no damage on Zilean Q and no damage that I can see coming in from minions. Here's a link to the video of it happening (behind the tower) around 6 seconds in: https://youtu.be/IH-JuC59NTM

Thanks!