What mysterious artillery is hitting me?

I was just in a battle against [UFTW]olympien and immediately after the game starts, my armstrong guns come under fire from some mysterious artillery. Based on the range involved, it's not armstrongs or parrotts or anything else conventional, and it is also not your normal naval bombardment which he employs a little later. I have included the replay; what on earth is hitting my general and armstrong guns?? I am baffled! mysterybombardment.replay

EDIT: In case no one wants to download the replay and check it out, there is no point of origin for the fire my general & armstrongs receive. I can see the shot come in, but each shot seems to be at a different trajectory and as best I can tell, originates off of the map. But again, it's definitely not naval fire as that is not immediately available or capable of sustained fire as this is. It's not kisho ninjas, and it seems like he has managed to place some kind of infinite-ranged artillery outside the normal play zone somehow! What in blazes is he using, and how can I employ it?