The pact that Germany and Austria-Hungary had didn't specify that part.
In any case, Germany was willing to stay neutral, until Russia declared war on Austria-Hungary.
But Germany wasn't the cause of WW1 - that was Austria-Hungary and Russia going to war over Serbia, and the other Great Powers getting pulled in due to their network of treaties.
Making everyone believe something false achieves nothing useful there.
I get the impression that for some of the people in the establishment of that day, the German Empire's real crime was existing at all. Bismark and his machinations upset the older status quo in many ways.