The closing item on The World at One was about just that 'football match' at Christmas.
Seems that there may have been a kick about for a few minutes but the whole Christmas lull in hostilities was used by both sides to bury the dead, some of whom had lain for weeks, possibly longer.
it is a social construct stoo, It was covered in the great serial on the great war in 1964 but in a few minutes ( episode 5 of thirty )
Survivors ( remember there were Boer War veterans around but not many) said Oh yeah there was a bit of that .....
as for the Germans saying the Armed forces have no function in normal society - well good one - Prussian Army was all powerful at that time. They are clearly rewriting History