Steam force every single game to be updated for multiplayer purposes, even singleplayer games has forced updates.
The option "do not automatically update this game" simply means that it wont update untill you click play.
I know useless right ? and if you put the game in offline mode you won't get achievements.
I usually crack the games i purchase or save a backup copy, cause i know how steam works by now.
Are you sure, because Company of Heroes 2 never updated for me unless I told it to update...??
I wasn't expecting today's unscheduled update of Rome 2. I normally have my steam client in offline mode for new releases.