A similar problem I’ve ran into both in tech support and user studies is momentary blindness for the scope of search. For example on your Mac, you have Spotlight, Finder search, Google search, help menu search, and various application-specific or website-specific search fields. In my experience if two of those are on screen at the same time, it’s very easy to get confused about which one to use to get which type of result.

You don’t need to be a naive user to make this mistake. The problem is that your brain is thinking “search”, your eyes are looking for something that looks like a search input, and when you find one you click it and start typing.

I feel like that’s what’s going wrong in this example too; it’s not that people expect Amazon to bring them to any random webpage, it’s just that there are two similar looking text inputs very close together on the screen.