""fortunately, no one was killed" Is a bit of give-away"

Only indicates that the gun did not have to be fired.

After the 1914 Christmas Truce orders were given that there should be no reccurrence, trench raids and actions were deliberately planned and timed so that it could not happen again they also gave orders that artillery and the machine gunners were to fire off salvoes every few hours over the Christmas Period including throughout Christmas Eve and Day. Appparently this isolated instance in 1915 didn't in anything like the scale and form of what happened in 1914 - the account in the link basically says so.

Captain Ian Colquhoun and Captain Miles Barne of the Scots Guards were Court Martialled under what charge Raggy? You forgot to mention it, so I will - Both men were charged with:

"Conduct to the prejudice of good order of military discipline in that on 25th Dec he (1) Approved of a truce with the enemy (2) Permitted a cessation of hostilities".

He did that for one reason and one reason alone - so that the Germans could collect and bury their dead who were lying in "no mans land".

Oh by the way Raggy Sir Ian Colquhoun in his diary entry for the 25th December 1915 specifically states that during the 45 minute "Truce" period Not a shot was fired The only shots actually fired that day were fired later on at night when the Germans put "fairy lights" up and the machine gunners fired at them from the British Trenches, this resulted in the lights being taken down.