A lot of torrenting clients leak information around your VPN connection. For instance, some torrenting clients send your actual public IP address through your VPN connection to seeders/leachers. There are companies that monitor torrenting, who see your public IP address and send a DMCA notice to your ISP, who forwards that notice to you.

Here's a related article for more information: https://blog.torproject.org/bittorrent-over-tor-isnt-good-idea/