If you cast a spell on the doorway of a shopping mall that is designed to explode if anyone opens it, then you should get a Lawbreaker, even if the proximate cause was the shopper choosing to walk through your booby-trapped door.
Similarly, the ward described was specifically designed to kill people, and was activated with the expectation that mortals would be triggering it in the near future.
You might be able to convince a Warden it was a accident/misunderstanding/whatever. Maybe. But the (metaphysical) Laws of Magic can be lawyered on technicalities. If you are the sort of wizard who would put into place a lethal ward knowing full well that it would be triggered by mortals with lethal consequences, then enjoy your Lawbreaker and new and improved aspect reflecting your shifting attitudes toward cavalier use of lethal magic.