You bound torrent client to tun0 You bound VP to tun0
If VPN is on, torrent client connects using VPN. If VPN is off, torrent client cannot connect to VPN or internet.
This is what should happen. It would be more helpful if you told us what you want to do. Do you want the torrent client to keep downloading but no longer behind the VPN? Because most people don’t want that. Which is why they set it up your way. Just in case the VPN accidentally goes down, you dox yourself.
Also a point I haven’t seen made, but a website is not torrent traffic. You could be behind a VPN through your browser but not through your torrent client (Apple’s Private Relay does this, only blanking you from websites). So the fact your torrent client stopped and the web was working seems to point to everything working as it should. You shouldn’t lose any internet unless it’s also bound to tun0.
Also, what did you use to create the tun0 interface to bind your client and VPN to?