Ah, my bad. Could have sworn they were an indexer; but it's been a while since I've used torrents.
"several sources" is rather... 'trust us'. Not a fan of that kind of reporting. But I know what you download is something at least.
That expands the scope to several public indexer sites instead of just one, but it's still only public peer-to-peer (torrent) traffic being measured. Usenet, direct download, private/pirate streaming, and private peer-to-peer are still left out.