Indirect confirmation: http://www.worldofmeh.com/wp-content/uploads/2010/06/civv4.jpg
Cannon is ready to fire and, since it has 1/2 movement, I assume it just moved.
Hmm... or it could be the set up, which took this movement point?
Hmm, that's in the video I was just looking at in the other thread, and the cannon does indeed fire with only 1 movement point. However, you don't see the cannon actually moving before it.
Maybe this was in the closed demo footage. I'll check now, but the movement point being used by setup sounds plausible IMO.
EDIT
Ok, so in the demo you also don't see the cannons set or move before-hand, so it's still up in the air.