Irrelevant to the question of "IF", relevant to the question of "HOW". In essence, what I'm saying is that both of you are right, just in the context of two related but different questions.
I was right with you on this, until I just updated Steam. Now, there's no option to prevent updates, only the following choices:
Always keep this game up to date
Only update this game when I launch it
High Priority - Always auto-update this game before others
Hopefully it's a glitch that they'll soon fix.
