Of course steganography is old, both as a concept and as tools to accomplish it. The article says this is the first time it's actually known to have been used

Of course steganography is old, both as a concept and as tools to accomplish it. The article says this is the first time it's actually known to have been used for nefarious purposes. That doesn't exclude prior usage for fun and experimentation, or even for practical purposes (say, wartime or corporate communications).