If you have a processor with multiple cores, it will offload the extra work onto the extra cores, just as it will with any game.
Well, actually the game can only use 2 cores to any great efficiency, and only 1 if you're a multiplayer client (rather than the host, which has a separate thread for the AI). There are a few other threads for audio and whatnot but they generally have trivial load.
That said, generally if you're running a multiplayer game as a host you want at least 3 cores, 1 for the main thread, 1 for the AI thread, and 1 for everything else on your system. With just 2 cores you'd have conflicts with the OS, etc.
Well yes, the game is threaded for 2, but most multi-core processors will offload extra work to other cores with relatively good efficiency.
I think the words you're looking for are actually "extremely poor efficiency". There's a reason a lot of stuff doesn't benefit from more cores/processors much, and that's that it's not written to use more threads well/effectively/at all, because that's frequently hard, especially if you didn't design with that in mind. No matter what kind of fancy tricks your OS and/or hardware try to pull, a single-threaded app is going to largely ignore anything beyond the core it's running on, aside from the benefit of not having to fight for it with other processes that can be stuck elsewhere. And no matter how many threads you do use, if they're all sitting around waiting on a single one that does most of the work and blocks everything else until it's done, that also results in it not really mattering how many cores you throw at it.
Claiming AI War has better threading than AAA games is also a little silly, too. AAA games from a few years ago before having multiple cores was common, sure (which is why older games still benefit a lot more from faster individual cores rather than more of them), but not newer ones. Most of them
require at least two cores these days to even be playable, and several of the more recent ones benefit noticeably from having four rather than two. Multi-threaded game programming has come a long way now that most PCs and all the non-Wii consoles pretty much need to take good advantage of it to get acceptable results.