Initial Intelligence. I already regret including it
More seriously, this is an interesting question. What differentiate a Dumb Sapient from a Smart Non-Sapient ?
First, what is Sapience ? According to some, Sapience is an additional property different from Intelligence. Sapience etymologically means wisdom, as per the latin word it is derived from. It is basically the ability to judge and to make choices. To think for one self, the notion of morality and good/bad.
Now what is Intelligence ? To simplify greatly, Intelligence is the ability to process information, gather and use knowledge in different ways. So Intelligence would be akin to the CPU and Memory of a computer to be very crude.
So a Smart non-sapient would be able to learn a lot of informations, to devise imaginative and unexpected plans. And if it were given a choice, it would follow its "natural programming". Survive, protect one kin, etc... It would be akin to a computer.
Still with the computer analogy, a Sapient, be it Dumb or Smart, would be able to question its programming. A Non-Sapient would never question its programming, as in Primal Needs or Genetic Behavior.
Of course, this is just my own interpretation, that myself knows if far from right. But it is to give a better idea of how I see Sapience and Intelligence in the boundary of this game's Universe.
tldr:
Sapience = Wisdom and Judgement
Intelligence = Brain Power
Smart Non-Sapient : Good Computer
Dumb Non-Sapient : Crappy Computer with a very complex Software installed