That is when they had the soccer game. After that incident, both the Germans and the British had to move the troops involved to another area. They basically refused to fight each other.
PS; The Germans still claim they won the soccer match.
If you are interested in read a very well researched book on the Christmas Truce, get Stanley Weintraub's, Silent Night, The story of the World War I Christmas Truce.
The Christmas Truce was portrayed in the movie "Oh What A Lovely War". The movie was a rather facetious semi-musical, but the Truce scenes were much like those described here. One of my favorite lines was from a kilted Scot who said something like "We dinna start this, THEY did" (pointing to the nearby English).