Calm down, this is not false advertising
It is merely a bit of chaos release, after all it was actually meant to be release 6 pm GMT according to the Steam Store page. This is also why we don't got a CD key yet (thus Coop is only available over LAN).
Also, you may rest assured there IS multiplayer in the game. You can actually try it out: simply copy an MP map from another MoW game (assault squad works too) into your map folder. You can then start a multiplayer game over LAN on that map
And I tried it out - the MP is identical to MoW. That means (even without mod support) you can simply copy any map (any game mode) and play it with the Vietnam units.
I don't guarantee correctness of this post, I might have just said rubbish.