No, "mywifiext.net not found" message does not mean that your range extender has been delivered to you without having www.mywifiext.net setup page. User should have to be aware of the fact that no NETGEAR range extender is manufactured without being configured with www.mywifiext.net setup page.
www.mywifiext.net webpage is local webpage provided by NETGEAR for its user to perform multiple tasks such as launching new Netgear extender setup using www.mywifiext.net setup wizard, altering configuration of already setup NETGEAR range extender and much more.
In case you are getting message "mywifiext.net not found", this pertain to some common mistakes done by user. For NETGEAR range extender troubleshooting you can follow article under "Related articles" tab.