The suspicious sites popping up in my about:networking page are the ones I mentioned. The strange torrents (most of which were infomercials, scam software, and video guides) downloading themselves happened once.
I don't think anyone accessed my computer because when I came back everything was the way I left it (except for the flood of new torrents that I never opened). I use qbittorrent often and I usually leave it running even when I'm not downloading anything. The torrent site I always use is rutracker.