They claim to know how Tor works, which means his network is a _relay_, not an origin, and that by Tor's nature it would have no record of the file passing through, when it happened, or more importantly where it was from. Cursory knowledge of how Tor works would tell you that this was a dead end before they left the station. IMHO it's clear this is an attempt to try to hold Tor operators responsible for the traffic of the Tor network, and in so doing, dissuade people from operating Tor endpoints. There is no other reason for this action, it's good old fashioned scare tactics.