BitTorrent Automatically Installed on MacOS High Sierra
Sorry to say this but the only way to get a bittorrent client installed with macOS is if you get it from anywhere but the Mac App store.

Note that macOS High Sierra is free from the Mac App Store. So there is no reason to get it any other way.

On the off chance that you did install from the Mac App Store it is likely that the bit torrent client was installed previously via some other means, possibly as a Trojan or virus of some other type.

If I were you, I would boot into recovery mode, reformat your hard drive and install everything from scratch. Hopefully you have a good uncontaminated backup.