that article suspiciously barely even mentions the winter solstice! (it is also a fairly Christian-biased article)
Saturnalia always falls on December 17th, while the solstice almost always falls between the 20th-23rd.
In the Celtic countries and England, there is a fair amount of archeological evidence suggesting pre-Christian observance of the solstices..and earlier myths paralleling the birth of the Christ were centered on solar gods; the appellations of 'god of light' and the 'light of the world' suggest the solar origin of this date as well. Also,the secular use of evergreen and lights for decoration which has continued for centuries until this day suggests a more likely connection to these solar-derived seasonal festivities, and not to Saturnalia...
I recommend a book by historian Ronald Hutton, Stations of the Sun, for specific explorations of folk custom and archeological evidence as the bases for Christmas (and other holidays).