Getting a dodge penalty for seemingly no reason? Did it change?

My friend and I were just queued to play Poro King. He had picked a champion, as did I. The game was just about to enter 'finalize your builds' stage when the lobby closed, and we were informed that he had apparently left the game... which he definitely didn't. Now we need to wait 15 minutes to queue again.

Did I miss something? What happened here? Was it because he hadn't locked in? Because I'm pretty sure in all my years playing League that that didn't count as 'leaving the game', and that normally it just locks in for you...