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

But if something such as Distintigrate or Power Word Kill, kills a creature instantly, is it specified in the rules that the creature “drops to zero hit points” (thus triggering any effects based on that condition)?

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.