I know a sex offender, who never interacted, only viewed CSAM. He was watched by the feds for 2 years, they monitored his viewing. The minute he downloaded one file they swooped. From what I understand the downloading is considered intent to distribute, which is a bigger concern than the viewing, to the feds at least.
I think Josh had allegedly downloaded a very large collection, so IMOO he would have had plenty of backlog to view over the 2 years since the download. Perhaps he decided to share one of his downloads, and that distribution triggered the arrest.