Warwick stopped being an active unit during his ultimate

During a fight my Warwick reached full mana and I was using the 1/2/3 keys to check out other players, I heard Warwick's ult go off and later moved my screen back to my board - I had a couple of units left fighting but Warwick was afk on full hp. After my other units died my opponent was awarded the win for the match, and my Warwick was still stood there looking kinda dumb. Managed to take a screenshot but a little too late - if you look carefully you can see the 4 blue swirls of the enemy player's units being teleported away. Next round everything was back to normal. Weird bug.