This is quite interesting, honestly. I assume “drachen” first and foremost meant dragon; if you run it by Google Translate, that is in fact exactly what you get! What is more interesting, however, is – if I may make some assumptions here – that the word “kite” may have very well been derived from dragon-themed kites, which is pretty cool. I’ve mused about some of my own settings in the past, and one of the items of interest was the language. In part, some of the things I thought about is where words came from or derived from. The example you have here is probably a real-world example of that!
Next, is there an available translation of the caption beneath the image? If not, I’d assume with this being a war manual, it was either used for signaling or for psychological operations. The latter is actually fairly plausible if you have a set of adversaries who have never seen a kite before. Add in a few extra ploys (like arson), and you could cause a good bit of mayhem – as long as the ones running the ploy don’t get caught.