Good catch. Thorium can't be used to produce weaponizable plutonium. My recollection is:
P-239 is weapons-grade plutonium.
U-238 is weapons-grade uranium.
P-238 is an alpha emitter, degrading to U-234(5?) (i.e. it skips U-238).
Thorium produces P-238 (and not P-239/U-238), so it is not useful for nuclear fission weapons.
In any case, I recall back in the debate about uranium or thorium reactors, DoD refused to produce Thorium precisely because they cannot be used to produce nuclear weapons.