It is a public holiday though, it's a half day off. And, as I've detailed, other countries that do not have public holidays are included.

Taiwan is colored red, even though not everyone gets the day off

edit: another example of being red despite not being a "total public holiday"

As far as I can see, Denmark hasn't officially "marked" the day as a public holiday, but I've tried to detail how that seems to be an inconsistent criteria in the list.