The IP leaks through the name of the page on the URL preview. https://iknowwhatyoudownload.com redirects to https://iknowwhatyoudownload.com/en/peer/ which includes the IP of the sender. The name of the page includes the IP address of the sender. "Torrent downloads and distributions for IP 0.0.0.0". If you paste the URL in a sentence with a period at the end this preview may not be generated.