sorry it's not a lie, you've been fooled by the propaganda bandied about by his descendants. The facts speak for themselves, he was emperor, his troops used poison gas, and he didn't forbid it. But in his defense, just about every other army in that war used it too.
You're the one who's been fooled by leftwing antiroyalist propaganda. Day-to-day military operations were not under the direct control of the Emperor. Karl came to the throne in the middle of the war and did everything he could to end it. As you admit, all the armies used poison gas. What makes the Emperor exceptional, in addition to his personally saintly character, was that he alone of all the leaders of that time was committed to ending the war.