IIRC, under neutron bombardment, Th233 becomes U233, which is fissile
thus the need for a breeder reactor
I think Th233 is fissile too, it has the correct physics. There may be issues that make it less practical than a U bomb, but to dismiss Th as “not fissile” in the article is wrong, or deliberately misleading.
Many actinide isotopes have the potential to go Pop. Manhattan project picked the most practical ones they could that would have a short development time.