Despite the translated wording, I definitely take it to mean that "up to Black Swordsman arc" means means "including Black Swordsman arc."
As for the picture of the berserker armor, either my memory of the timeline is fuzzy but I think that comes way later. Attack on Titan musou had a couple extra side missions with that jumped around in continuity, so it could be the same here.
I'm not sure it's the Berserker armor, looks like his blacks swordsman armor but it's so damn blurry I can't tell.