The campaign is dynamic because you can go whereever you please and you don't get scripted orders(or do you? don't have the game yet)
Also, the location of the enemy is (mostly) ramdon.(again, not certain)
example:
You head for Australia, you meet a Task Force with a carrier on the way. This little meeting was not scripted for you, maybe it was supposed to be there at the given time, but the player could have been on the other side of the ocean as far as the game knows. And the game won't spawn in ships just because you're bored and haven't met anything in weeks (this is the case in SHIII,where I would often be without a single contact for 7-14 days....)
OFF TOPIC:
Another game with a good "dynamic" campaign? Combat Flight Simulator 3. I remember looking at the status of an enemy airfield, and it said: "Fighting strength: Bf-109:100%" or something like that. So when I went to the area to bomb a factory I also decided to have a go on the enemy airfield.
So I destroyed every aircraft on sight, then dropped my bombs on the factory (or vice versa, don't remember) and headed home. Then after an update I checked the enemies airfield status: "Bf-109:9%"
So I didn't destroy them all, but maybe some of them was in the sky somewhere during my attack. And the enemy air resistance was very limited in the area after my attack.....
That's what I call dynamic!
