Yes, this is good news. To sum up, Sailfish OS is not vulnerable, as the DHCP option 121 is not read from DHCP packets.
This can be verified by anyone willing to do so with the instructions setup by the organization who found and published the issue: GitHub - leviathansecurity/TunnelVision: A network technique that decloaks a VPN users traffic on a local network without disconnecting them from a VPN.