what training scenario were they doing
As reported the days before (translated from German):
According to the Bundeswehr, the deployed forces are to train operations against threats behind a fictional front line, in what is referred to as the "rear area." This includes scenarios involving drones, sabotage, or so-called "irregular forces," meaning armed fighters not belonging to a state army. The assumption is that a NATO member state is attacked, and the alliance must respond to defend it.
Training will also focus on tasks such as working at crime scenes, directing traffic, locating weapon caches, combating illegal arms trade, and protecting critical infrastructure, for example, at the decommissioned Isar 2 nuclear power plant. Soldiers will also practice defending against enemy drones and deploying their own.
I suggest waiting for the report of the official investigation.