That is what I thought - looks like some kind of live-fire exercise.
I find the claim of the army seizing servers dubious as ai highly doubt the state of Germany would be so permissive. It's not impossible - it just seems like an extremely odd event.
It's been floating around for a few days now as "breaking" news, so I am geberally going on the side of disinfo - but it could be interesting if the systems were "cloud" based and hosted/mirrored at a foreign location. So that part is curious.