It doesn’t matter if the mage could have avoided it, was tabbed, fell asleep, etc…if another player purposefully creates a situation that leads, or ostensibly could lead, to your death, by definition that is griefing and should be subject to review and/or discipline.
The fact that the player who died did not, or could not, escape the situation does not expiate the guilt of the person who dropped the mobs on him. So, bringing up the point that he could have survived is quite literally victim shaming. Maybe he shouldn’t have worn that short dress, I guess.