People from Ireland (including Northern Ireland) would notice immediately what's wrong. People from GB really should notice what's wrong, though the actual office of the UK PM went ahead and published the video - an official video without noticing what was wrong.

It would probably be unreasonable to expect people from further afield to notice.

The map shows the UK having - apparently - re conquered a county of the Republic of Ireland. Quite a big county. It's perhaps as if the White House published a map of the USA showing it occupying the section of Canada from Windsor to Toronto.