Graves Q question

So I just played a game as AP Graves (Accidentally had wrong runes and masteries so I went with it) and noticed that my Q procced the Luden's Echo passive. I was wondering if this was intended to be part of the game? I didn't think this was a bug because of the wording of the Luden's Echo tooltip saying "next spell" but just wanted some clarification. Match history linked to prove I had the item. Sadly it was my last item so I didn't get an image of the incident.