The issue is on the host’s end. They have most likely put the wrong local IP into the server.properties file. Have your friend find the line that is server-ip=
and have them put the IP of the VPN’s network interface if it has one. That should make it so that the traffic for the minecraft server is through the VPN instead of though their real network.
But it would be unwise to trust them again. They could change their minds at any time, just as they did before.