No doubt those images downloaded themselves just like Baldwin’s self-firing gun and that SUV that drove into the crowd in Waukesha.
I have no knowledge or opinion of Josh Duggar’s pedophilia or child porn predilection, but just like manipulation of digital images, audio, etc, I am naturally skeptical of damaging evidence “found” on someone’s computer. Given the skill of hackers and the resources of government, it would be a trivial exercise to plant it there.