Correct, but in this case, it sounds like you didn't need to use the ISP router as your VPN gateway.
If I understand the DNS rebinding attack reference correctly, you could be running the VPN software on your desktop/laptop and still have your IP revealed by your ISP router.
If I understand the DNS rebinding attack reference correctly, you could be running the VPN software on your desktop/laptop and still have your IP revealed by your ISP router.