If he is going to discuss definitions, agnostic seems to fit him better.
Spot on.
Theists have faith - that is Theists believe God exists without proof
Atheists believe in the non-existence of God.
Agnostics do not “believe” as in having “faith” (belief without proof). Agnostics require proof.
By his definition of his belief set, Jillette would be an Agnostic.