It also depends on the latitude and longitude of the observer.
People in the southern hemisphere would see their "shortest day" of the year on or around June 21st.
And by "shortest day", I assume that you actually mean "day with fewest hours of solar illumination".
_________________
The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.