First, they only see the endpoint IP. There could be hundreds of computers behind that IP. Got Wifi? Your neighbors could use it to download a copyrighted work. Why are you to be punished for someone else hacking a badly put together wifeless device that AT&T provided you?
Without deep packet inspection, there is no way to determine which computer behind the public IP is making the illegal connection.
Second, simply because you are connected to and receiving data from an IP known to be hosting a copyrighted work, it does not necessarily follow that the file you are receiving is a copyrighted work. It could be a user created video shared from the same IP. Again, without deep packet inspection, there is no way to know which is which.
Finally, if you accuse a customer of committing a crime with no evidence to back up that claim, you may be committing an act of defamation.
