qBittorrent official forums

This is just a matter of curiosity rather than a concern. I always try at least not to be a complete leech considering that it endangers the filesharing community, but for some reason, even behind a VPN that doesn't support port forwarding, I somehow seem to be able to upload a certain amount, enough to get at least a 1/1 ratio so I can just seed the torrent up to the proper ratio that I'm not just a leech.

I just have to leave the client open, but much longer than it took to download.

How does this work? Is there a way to make it better and actually use a VPN while not just being a leech?

It works because the endpoint of your VPN has ports open that peers can connect to.

You would need a VPN port forward if you wanted to run a service on your end of the tunnel and make it available via the VPN IP address instead of your own IP address.

Your VPN can make outgoing connections to peers that are not firewalled...and it is to those that qBitTorrent is able to upload to.

There is also a remote possibility that uTP's STUN-based hole-punching works even through the VPN, but that requires VPN support for conditionally opening UDP ports at its IPv4 location and even some luck.