I told that I need to:
1. navigate to this page, testing all pages on its way.
try all available way how can I come to this page #3, inlcuding direct url copy/paste.
2. actually test this button (functional test)
3. navigate back from this page.
That's nice and very robust, but why test everything on the way to the designated object? Your goal is to test the pushbutton. Be explicit with your preparations. With your answer the interviewer could be thinking: "so what if he hits a defect in a previous page and never gets to the 3rd page to test the button. He could take forever just setting up the test environment. Just my opinion but it might be worth considering.
Success is the ability to go from one failure to another with no loss of enthusiasm.
~ Winston Churchill ~