In Norwegian we use the terms "Christmas calendar" and "Advent calendar" (translated directly) interchangeably. This i probably why some of the calendars (under the https://bekk.christmas umbrella) are using the term incorrectly
I don't really think the difference is really notable. I knew it would be a daily calendar counting until Christmas. I guess I fall into the camp of not being a prescriptivist of language.
Edit: on second thought, i guess you've meant "Machine Learning Christmas" Calendar. That's fine. It just bothers me a bit that in the US people forget about Advent.