Why the calendar app has random dots under it

Click on the three dots in the upper right corner and select "Show agenda" and you'll see the calendar items for the selected day. It's basically a bunch of "National X Day" items. 

If you see a dot under a date, it means you’ve got something planned or scheduled—could be a meeting, a birthday, or a reminder. If there are multiple dots, it just means you’ve got several things going on that day.

what does that dot mean? ha ha, I never meet this!