Each hop is encrypted between nodes at the connection layer… An ISP or any other relayer or snooper could not identify any chunk as it is encrypted between network nodes.
So, assuming that one of the network nodes along the way was sniffing for particular chunks that had been identified as being part of a secret or illicit file, it could tell that it was receiving that chunk from a node with an IP address in its routing table and was passing it on to another node in its routing table. It wouldn’t be able to determine where it was stored or who requested it.
Even if it sent it to you and you had requested it, the snooper node couldn’t tell whether you were the destination or a relay.
I believe it is even more impenetrable than that but don’t have time to run it down right now. Check out this post on layers of encryption: