It's more a failure of mechanical expression (IMO) than anything else.
The point of it is to have some monsters where any hit by a sufficiently powerful enemy will kill them. It's the exact same logic used for unsurvivable fall damage and instakill assassination attacks (not that I'm particularly fond of these, but they do serve as existing precedent).
But instead of describing the instakill effect and its parameters (i.e. how much more powerful enemies must be to kill with a single attack), the designers chose to use the hp system instead, causing all this confusion about the underlying objective nature of these creatures and concern about the newfound lethality of housepets and woodland creatures.
But the instakill effect is a reasonable bit of genre emulation that could exist in the game and mostly doesn't. I think it could be fixed fairly simply if folks were willing to agree on the parameters for when it should trigger rather than worry about rodents with an axe to grind.