You are jumping to speculations and ignoring the facts in front of you:

1. OpSec Online Antipiracy detected the download, not Xfinity
2. Bittorent clients have to know who is serving what content (that's the whole point of P2P networks)

So, by checking out the company, they say:

OpSec® PeerScan enables you to protect your content against Peer-to-Peer (P2P) piracy abuse. Its unique intelligence enables you to see the number of peers connecting to a swarm, their geo-location, title, asset quality, and language ...

and then

Industry-leading BitTorrent Level 1 public trackers and Distributed Hash Table (DHT) client designed from the ground up to provide excellent scheduling and data capture capabilities.

and

Powered by OpSec® PeerScan, OpSec® Acuity Pro systematically monitors an index of music, film, and television titles worldwide to provide visibility into piracy consumption across different markets and media on file-sharing networks. This data helps you gain a deeper understanding of when, where, and how copyrighted content is being used

So, it's all quite simple: OpSec Security simply watches active BitTorrent traffic, as anyone can do from their own BitTorrent clients, and reports to copyright holders.

You are jumping to speculations and ignoring the facts in front of you:

1. OpSec Online Antipiracy detected the download, not Xfinity
2. BitTorrent clients have to know who is serving what content (that's the whole point of P2P networks)

So, by checking out the company, they say:

OpSec® PeerScan enables you to protect your content against Peer-to-Peer (P2P) piracy abuse. Its unique intelligence enables you to see the number of peers connecting to a swarm, their geo-location, title, asset quality, and language ...

and then

Industry-leading BitTorrent Level 1 public trackers and Distributed Hash Table (DHT) client designed from the ground up to provide excellent scheduling and data capture capabilities.

and

Powered by OpSec® PeerScan, OpSec® Acuity Pro systematically monitors an index of music, film, and television titles worldwide to provide visibility into piracy consumption across different markets and media on file-sharing networks. This data helps you gain a deeper understanding of when, where, and how copyrighted content is being used

So, it's all quite simple: OpSec Security simply watches active BitTorrent traffic, as anyone can do from their own BitTorrent clients, and reports to copyright holders.