The typical way to die involves dropping to zero hit points first.

But if something such as Power Word Kill, kills a creature instantly, is it specified in the rules that the creature “drops to zero hit points” ?

To clarify, I understand that dead means dead, and dead creatures do not get to make death saving throws. The question is, does the act of a creature dying make its hit point total zero?

Or can a creature simply “die” (and then, perhaps, have no hit point total?) thus skipping any effects triggered "when [this creature] drops to zero hit points."

The recent question about Paladin’s Steed is the inspiration for this question. I know I would rule that getting dead means going to zero hit points — I just haven’t seen that said as much in official material.