Caretaker was senile, and before he was senile, he was the least useful member of the Nacene exploration into the Milkyway which is why he was abandoned to look after the Ocampa. I'm thinking that he was possibly the janitor or a prostitute who was charged with keeping Susperia sexually placated, unfortunately before he was senile he was such a terrible companion that Susperior took some Ocampa and ran away so well that he couldn't find her after hundreds of years even though Janeway ran into her after just over a year.
He's quite dim.
The actual scoop which he used to gather his rapees is the device I was saying that he didn't recalibrate, just like some times we don't refocus our binoculars between different ranges if it's "close enough".
Why banjo Man, why the farm, and why the early 20th century?
If he scanned the ship's computers, he would not have tailored his illusions to create Banjoman, the farm or the 20th century... Even if Tom was unbuckling his pants at some point during his incarceration since he didn't really know the difference between a hologram meant to keep him too impotent and distracted to plan an escape compared to 20th century poon tang on the pull.