I thought one of the sub-reasons for the creation of the Torrent system in the first place was plausible deniability over what you've downloaded? Unless it's an extremely rare thing being seeded by a single host and not shared even temporarily by others, your computer pulls in chunks from dozens of others in a semi-random fashion. Tracing the source of all those packets, and what's inside them, is the devil's own job; essentially, you'd have to already be under enough suspicion that your entire web traffic would be getting recorded man-in-the-middle style and the torrents you download reconstructed on the fly to see what's in them. Otherwise it's just a pattern of mass accesses to numerous other peers sending out packets of individually meaningless data (especially if it's a RAR/ZIP, doubly so if password encrypted) with no clear connection between them. It doesn't even necessarily download things in the correct order, it just takes chunks as they're available.

Anyway, if you're worried, delete the file, clear your Windows file history and that of the torrent client, and run a defragmenter that has the option to securely wipe all empty sectors after the run completes, e.g. Auslogics Disk Defrag. There shouldn't be anything left tying you to that file, or to suggest it was anything other than a passing Wifi leech who managed to break your router's encryption (WPA2 is starting to become rather weak vs modern processors and cracking techniques).