This wasn't the default autopilot but a new system, as such they didn't know what was causing the behaviour. On top of that all their sensors gave them different information.

> If the autopilot tries to screw things up it is standard procedure to turn it off. Is failing to do so is human error? I guess so.

You have a new automatic system pilots are not told about that will deep dive a plane with 200 people into the ocean unless you do things you have learned to apply in a different situation. I don't think you can call that a human error.. Except for maybe the human that decided not to tell the pilots?

And in the previous flight a similar team could handle it?