What is Captiveportal.Nokia.com?

It would seem you have tried to connect to a public wi-fi that uses a captive login screen. That address would allow one to log into a public wi-fi network that required a login.

If it is an annoyance,

1. Close all Safari tabs.
2. Settings, Safari, Clear all history and website data
3. Settings, General, Reset, Reset network settings

It should not bother you again