To be correct, it is involuntary manslaughter thruogh negligence (sounds different ?), if convicted they will be getting off on a fine.
Also, but on the same line, accusation is *NOT* an automatic conviction here in Spain no matter what uninformed sources might tell ya.
From the judge´s point of view, all he needs is indication for a crime (felony) to take action, and he has made it clear that he figures there are plenty of them (personally, I agree, but do not think it will lead to conviction as the main cause seems stll to be the misconfiguration in first instance).
Think of it a a court martial, keeping up the spirit while performing to the public, plenty of room still and nothing perjudicary stated with just the accusation.
The judge charging them with a homicide seems a bit extreme.