Enemy Player reads my teams chat

So today i was playing a game of aram with my group of 4 friends and my teams kat said something in team chat and the enemy sion instantly replied(No way it could have been a coincidence either). i'm not sure if this is a bug or something but since i was unsure i reported him with the description that it could be a bug. So I was wondering.... EDIT:So i may have just went back and read the rules for this part of the forum, and its the wrong one. So if this could be deleted it would be great xD

Is he hacking???

P.S. sorry if this is in the wrong thread.