This would be an interesting exercise in logical thinking if readers had not already been signaled that something is amiss. Also, the text used has been circulating in one form or another since at least 2015 (that is the earliest I could find). Take a look and see what is wrong with the text in this picture:
First of all, look at your calendar. It’s on a Monday. Second, Halloween isn’t a floating observance, but is always on the last day of October.
The Julian calendar was in use for a mighty long time, but became increasingly accurate. It was replaced by the Gregorian calendar beginning in 1582. So, there are not 666 years in this calendar system, and the typical “meme” maker does not bother with details involving calculating dates between Julian and Gregorian calendars.
Now, don’t be letting this put a burr under your saddle because I seem to be taking this a mite serious. That caption was clearly a prank, and kind of funny at that. This child wonders how many people believed it without bothering to use their think bones. What we have here is a very small example of how critical thinking applies in many areas of life.