your first clue might have been that it does not say "zip code" in either the field label or the error message, it says "postcode".
Australia and NZ have postcodes, too.
If they had made this a .co.uk rather than a .com, there would be no confusion.
The site has since changed the content from when I made the comment. It used to say zip code in the label and error.
Or the term "pub." In the US it's much more usual to say "bar." Maybe "tavern" but that sounds rather dated to my ear.
I doubt most people would bother to think about that detail.
I think of postal code as a generic, international form of the concept, not tied to a location.