The distribution is 100% what got him caught, and is the vast majority of prosecutions, but creation and possession is still separately illegal. And he didn't need to modify any OSS. Any image-generating AI is capable of generating such imagery. So too can anyone use Photoshop, or a paint brush, to create illegal imagery.
> A Florida man is facing 20 counts of obscenity for allegedly creating and distributing AI-generated child pornography
I'd bet distribution of CSAM the crime what got him prosecuted, not modifying OSS.