The most “hacked up” explanation I’ve yet heard for the calendar issue:
Today, in the Greek and Russian orthodox churches, Christmas is celebrated 13 days after the 25th, which is also referred to as the Epiphany or Three Kings Day. This is the day it is believed that the three wise men finally found Jesus in the manger.
Update: After leaving a comment about this error I received an email a day later from the author apologizing and promising to print a correction. There seem to be some journalists out there who can “get religion” with a little prompting.