Default behaviour for torrent software was to upload and advertise as well as download. This advertising of your IP and files is how the movie people make lists of "Who's distributing my stuff". They then lookup the owner of the IP address, which tells them the ISP. They contact the ISP. And these days the ISPs roll over with barely a whimper and give up your details. Or they send you an email. Or it can lead to ambulance chasing lawyer letters. And all of this is automated these days.
This is why people use VPNs and virtual servers these days. Or Netflix.
This is why people use VPNs and virtual servers these days. Or Netflix.