Tor network has only become "a thing" (as opposed to US military toy) only in the last few years. Half a decade ago such a log the police saw would probably be a clear-cut case of someone downloading or uploading child porn on the guy's network. Even with Tor being available, it's still worth checking out.

If they were that incompetent about computers they had no business running their own cp investigation. They would have mishandled evidence. They should have handed it off to the state police or the FBI.

Alternatively they could have just been bunch of dicks out to intimidate someone.