Game runs after closing and cannot relaunch game client(BUG)

During a recent ranked flex game, after champ select, my game client opened, then i tabbed out do pause the youtube video i was watching. After that i couldnt open the game client again and closed it, hoping to be able to open it up again from the client. After not being able to do this, i hear the begining of the game sounds, like then the champions pop into game for the first time, even though the game wasnt open, so i restarted my computer, and after it boots back up, i open league, and now i have a 20 minute leaver buster and i didnt leave intentionally, but it was a glitch with the new client,