Does anyone here know anything about this?

I know of no cases of 'decimation' ever being used in WWI, by any Army; that "fact", like that answer, is little better than hyperbole.

In fact, rumours spread in the outbreak of the French Army Mutinies of 1917 that decimation was being used, and aside from turning out to be completely unfounded, only made the situation worse. While the Italian Army did shoot more of it's own soldiers than any other power in the war, soldiers were not disciplined by being shot randomly en masse.

I will say, however, that the disturbing amount of misinformation about WWI that you could find on reddit is pretty neatly summed up in that "answer."

Leonard V. Smith's Between Mutiny and Obedience discusses the French Army Mutinies, and Richard Holmes excellent book Tommy gives some info about British Army executions.