The connection to this IPV4 seed wasn't established through the torrent client. This wasn't necessarily a failure of my firewall to prevent my torrent client from downloading from a non virtual adapter MAC address, as it is configured. However, my torrent was still downloading as I was still connected to a single IPV4 seed based in Sweden. I was completely disconnected from Softether VPN service, essentially. My browsers and other web based services were making direct connections to the internet using my actual IP address as confirmed by my firewall. The Softether VPN Client Manager console window showed no active 'VPN Gate Connection'.

However, I recently encountered a relay server based in Japan that disconnected me while I was still downloading a torrent file. Therefore, if I should lose my connection to a VPN Gate relay server, my torrent client becomes inactive and doesn't resume connections through my regular network adapter's hardware MAC address. I've customized my firewall to only accept incoming and outgoing connections to my torrent client originating from the virtual Softether vpn client adapter's MAC address. I used Softether with VPN Gate to download a torrent.

Using latest Softether 4.18 Build 9570 with the latest available VPN Gate plugin

Softether vpn gate plugin